Stems Cells and the Pathways to Aging and Cancer

Low-Dose Pesticide Mixture Induces Accelerated Mesenchymal Stem Cell Aging In Vitro

The general population is chronically exposed to multiple environmental contaminants such as pesticides. We have previously demonstrated that human mesenchymal stem cells (MSCs) exposed in vitro to low doses of a mixture of seven common pesticides showed a permanent phenotype modification with a specific induction of an oxidative stress-related senescence. Pesticide mixture also induced a shift in MSC differentiation toward adipogenesis. Thus, we hypothesized that common combination of pesticides may induce a premature cellular aging of adult MSCs. Our goal was to evaluate if the prolonged exposure to pesticide mixture could accelerate aging-related markers and in particular deteriorate the immunosuppressive properties of MSCs. MSCs exposed to pesticide mixture, under long-term culture and obtained from aging donor, were compared by bulk RNA sequencing analysis. Aging, senescence, and immunomodulatory markers were compared. The protein expression of cellular aging-associated metabolic markers and immune function of MSCs were analyzed. Functional analysis of the secretome impacts on immunomodulatory properties of MSCs was realized after 21 days' exposure to pesticide mixture. The RNA sequencing analysis of MSCs exposed to pesticide showed some similarities with cells from prolonged culture, but also with the MSCs of an aged donor. Changes in the metabolic markers MDH1, GOT and SIRT3, as well as an alteration in the modulation of active T cells and modifications in cytokine production are all associated with cellular aging. A modified functional profile was found with similarities to aging process. Stem Cells 2019;37:1083-1094.

Modes of division and differentiation of neural stem cells

Hippocampal neurogenesis presents an unorthodox form of neuronal plasticity and may be relevant for the normal or abnormal functioning of the human and animal brain. As production of new neurons decreases after birth, purposefully activating stem cells to create additional new neurons may augment brain function or slow a disease's progression. Here, we describe current models of hippocampal stem cell maintenance and differentiation, and emphasize key features of neural stem cells' turnover that may define hippocampal neurogenesis enhancement attempts' long-term consequences. We argue that even the basic blueprint of how stem cells are maintained, divide, differentiate, and are eliminated is still contentious, with different models potentially leading to vastly different outcomes in regard to neuronal production and stem cell pool preservation. We propose that to manipulate neurogenesis for a long-term benefit, we must first understand the outline of the neural stem cells' lifecycle.

Homeostasis and systematic ageing as non-equilibrium phase transitions in computational multicellular organizations

Being a fatal threat to life, the breakdown of homeostasis in tissues is believed to involve multiscale factors ranging from the accumulation of genetic damages to the deregulation of metabolic processes. Here, we present a prototypical multicellular homeostasis model in the form of a two-dimensional stochastic cellular automaton with three cellular states, cell division, cell death and cell cycle arrest, of which the state-updating rules are based on fundamental cell biology. Despite the simplicity, this model illustrates how multicellular organizations can develop into diverse homeostatic patterns with distinct morphologies, turnover rates and lifespans without considering genetic, metabolic or other exogenous variations. Through mean-field analysis and Monte-Carlo simulations, those homeostatic states are found to be classified into extinctive, proliferative and degenerative phases, whereas healthy multicellular organizations evolve from proliferative to degenerative phases over a long time, undergoing a systematic ageing akin to a transition into an absorbing state in non-equilibrium physical systems. It is suggested that the collapse of homeostasis at the multicellular level may originate from the fundamental nature of cell biology regarding the physics of some non-equilibrium processes instead of subcellular details.

Head and neck cancer management and cancer stem cells implication

Head and neck squamous cell carcinomas (HNSCCs) arise in the mucosal linings of the upper aerodigestive tract and are heterogeneous in nature. Risk factors for HNSCCs are smoking, excessive alcohol consumption, and the human papilloma virus. Conventional treatments are surgery, radiotherapy, chemotherapy, or a combined modality; however, no international standard mode of therapy exists. In contrast to the conventional model of clonal evolution in tumor development, there is a newly proposed theory based on the activity of cancer stem cells (CSCs) as the model for carcinogenesis. This “CSC hypothesis” may explain the high mortality rate, low response to treatments, and tendency to develop multiple tumors for HNSCC patients. We review current knowledge on HNSCC etiology and treatment, with a focus on CSCs, including their origins, identifications, and effects on therapeutic options.

AMPK regulates germline stem cell quiescence and integrity through an endogenous small RNA pathway

During suboptimal growth conditions, Caenorhabditis elegans larvae undergo a global developmental arrest called "dauer." During this stage, the germline stem cells (GSCs) become quiescent in an AMP-activated Protein Kinase (AMPK)-dependent manner, and in the absence of AMPK, the GSCs overproliferate and lose their reproductive capacity, leading to sterility when mutant animals resume normal growth. These defects correlate with the altered abundance and distribution of a number of chromatin modifications, all of which can be corrected by disabling components of the endogenous small RNA pathway, suggesting that AMPK regulates germ cell integrity by targeting an RNA interference (RNAi)-like pathway during dauer. The expression of AMPK in somatic cells restores all the germline defects, potentially through the transmission of small RNAs. Our findings place AMPK at a pivotal position linking energy stress detected in the soma to a consequent endogenous small RNA-mediated adaptation in germline gene expression, thereby challenging the "permeability" of the Weismann barrier.

The Yin and Yang of RNA Methylation: An Imbalance of Erasers Enhances Sensitivity to FTO Demethylase Small-Molecule Targeting in Leukemia Stem Cells

A prevalent eukaryotic N⁶-methyladensosine (m⁶A) post-transcriptional mark can be "erased" by the m⁶A demethylase FTO, which is commonly deregulated in acute myeloid leukemia (AML). In this issue of Cancer Cell, Huang et al. design small-molecule FTO inhibitors, FB23 and FB23-2, and demonstrate their potent inhibitory impact in AML models.

Making Sense of Stem Cells and Fat Grafting in Plastic Surgery: The Hype, Evidence, and Evolving U.S. Food and Drug Administration Regulations

Autologous fat grafting and adipose-derived stem cells are two distinct entities with two different risk profiles, and should be regulated as such. Autologous fat grafting prepared with the additional step of stromal vascular fraction isolation is considered a form of "stem cell therapy" given the high concentration of stem cells found in stromal vascular fraction. Much ambiguity existed in the distinction between autologous fat grafting and stromal vascular fraction initially, in terms of both their biological properties and how they should be regulated. The market has capitalized on this in the past decade to sell unproven "stem cell" therapies to unknowing consumers while exploiting the regulatory liberties of traditional fat grafting. This led to a Draft Guidance from the U.S. Food and Drug Administration in 2014 proposing stricter regulations on fat grafting in general, which in turn elicited a response from plastic surgeons, who have safely used autologous fat grafting in the clinical setting for over a century. After a series of discussions, the U.S. Food and Drug Administration released its Final Guidance in November of 2017, which established clear distinctions between autologous fat grafting and stromal vascular fraction and their separate regulations. By educating ourselves on the U.S. Food and Drug Administration's final stance on fat grafting and stem cell therapy, we can learn how to navigate the regulatory waters for the two entities and implement their clinical use in a responsible and informed manner.

Delayed Effects of Acute Radiation Exposure (Deare) in Juvenile and Old Rats: Mitigation by Lisinopril

Our goal is to develop lisinopril as a mitigator of delayed effects of acute radiation exposure in the National Institute of Allergy and Infectious Diseases program for radiation countermeasures. Published studies demonstrated mitigation of delayed effects of acute radiation exposure by lisinopril in adult rats. However, juvenile or old rats beyond their reproductive lifespans have never been tested. Since no preclinical models of delayed effects of acute radiation exposure were available in these special populations, appropriate rat models were developed to test lisinopril after irradiation. Juvenile (42-d-old, prepubertal) female and male WAG/RijCmcr (Wistar) rats were given 13-Gy partial-body irradiation with only part of one hind limb shielded. Lethality from lung injury between 39-58 d and radiation nephropathy between 106-114 d were recorded. All irradiated-only juvenile rats were morbid from delayed effects of acute radiation exposure by 114 d, while lisinopril (24 mg m d) started 7 d after irradiation and continued improved survival to 88% (p = 0.0015, n ≥ 8/group). Old rats (>483-d-old, reproductively senescent) were irradiated with 13-Gy partial-body irradiation keeping part of one leg shielded and additionally shielding the head in some animals. Irradiated old females developed lethal nephropathy, and all became morbid by 170 d after irradiation, though no rats displayed lethal radiation pneumonitis. Similar results were observed for irradiated geriatric males, though 33% of rats remained alive at 180 d after irradiation. Lisinopril mitigated radiation nephropathy in old rats of both sexes. Finally, comparison of delayed effects of acute radiation exposure between irradiated juvenile, adult, and old rats showed younger rats were more sensitive to delayed effects of acute radiation exposure with earlier manifestation of injuries to some organs.

RnBeads 2.0: comprehensive analysis of DNA methylation data

DNA methylation is a widely investigated epigenetic mark with important roles in development and disease. High-throughput assays enable genome-scale DNA methylation analysis in large numbers of samples. Here, we describe a new version of our RnBeads software - an R/Bioconductor package that implements start-to-finish analysis workflows for Infinium microarrays and various types of bisulfite sequencing. RnBeads 2.0 (https://rnbeads.org/) provides additional data types and analysis methods, new functionality for interpreting DNA methylation differences, improved usability with a novel graphical user interface, and better use of computational resources. We demonstrate RnBeads 2.0 in four re-runnable use cases focusing on cell differentiation and cancer.

Adaptive endoplasmic reticulum stress signalling via IRE1α-XBP1 preserves self-renewal of haematopoietic and pre-leukaemic stem cells

Over their lifetime, long-term haematopoietic stem cells (HSC) are exposed to a variety of stress conditions that they must endure. Many stresses, such as infection/inflammation, reactive oxygen species, nutritional deprivation and hypoxia, activate unfolded protein response signalling, which induces either adaptive changes to resolve the stress or apoptosis to clear the damaged cell. Whether unfolded-protein-response signalling plays any role in HSC regulation remains to be established. Here, we report that the adaptive signalling of the unfolded protein response, IRE1α-XBP1, protects HSCs from endoplasmic reticulum stress-induced apoptosis. IRE1α knockout leads to reduced reconstitution of HSCs. Furthermore, we show that oncogenic N-Ras^G12D activates IRE1α-XBP1, through MEK-GSK3β, to promote HSC survival under endoplasmic reticulum stress. Inhibiting IRE1α-XBP1 abolished N-Ras^G12D-mediated survival under endoplasmic reticulum stress and diminished the competitive advantage of Nras^G12D HSCs in transplant recipients. Our studies illuminate how the adaptive endoplasmic reticulum stress response is advantageous in sustaining self-renewal of HSCs and promoting pre-leukaemic clonal dominance.

Adult Cardiac Stem Cell Aging: A Reversible Stochastic Phenomenon?

Aging is by far the dominant risk factor for the development of cardiovascular diseases, whose prevalence dramatically increases with increasing age reaching epidemic proportions. In the elderly, pathologic cellular and molecular changes in cardiac tissue homeostasis and response to injury result in progressive deteriorations in the structure and function of the heart. Although the phenotypes of cardiac aging have been the subject of intense study, the recent discovery that cardiac homeostasis during mammalian lifespan is maintained and regulated by regenerative events associated with endogenous cardiac stem cell (CSC) activation has produced a crucial reconsideration of the biology of the adult and aged mammalian myocardium. The classical notion of the adult heart as a static organ, in terms of cell turnover and renewal, has now been replaced by a dynamic model in which cardiac cells continuously die and are then replaced by CSC progeny differentiation. However, CSCs are not immortal. They undergo cellular senescence characterized by increased ROS production and oxidative stress and loss of telomere/telomerase integrity in response to a variety of physiological and pathological demands with aging. Nevertheless, the old myocardium preserves an endogenous functionally competent CSC cohort which appears to be resistant to the senescent phenotype occurring with aging. The latter envisions the phenomenon of CSC ageing as a result of a stochastic and therefore reversible cell autonomous process. However, CSC aging could be a programmed cell cycle-dependent process, which affects all or most of the endogenous CSC population. The latter would infer that the loss of CSC regenerative capacity with aging is an inevitable phenomenon that cannot be rescued by stimulating their growth, which would only speed their progressive exhaustion. The resolution of these two biological views will be crucial to design and develop effective CSC-based interventions to counteract cardiac aging not only improving health span of the elderly but also extending lifespan by delaying cardiovascular disease-related deaths.

Thymosin β4 for the treatment of acute stroke: neurorestorative or neuroprotective?

INTRODUCTION

Thymosin β4 (Tβ4) is a 5K peptide which influences cellular migration by inhibiting organization of the actin-cytoskeleton. Treatment of acute stroke presently involves use of rt-PA and/or endovascular treatment with thrombectomy, both of which have time limitations. Therefore, development of a treatment beyond these times is necessary as most stroke patients present beyond these time limits. A drug which could be administered within 24 h from symptom onset would provide substantial benefit.

AREAS COVERED

This review summarizes the data and results of two in-vivo studies testing Tβ4 in an embolic stroke model of young and aged rats. In addition, we describe in-vitro investigations of the neurorestorative and neuroprotective properties of Tβ4 in a variety of neuroprogenitor and oligoprogenitor cell models.

EXPERT OPINION

Tβ4 acts as a neurorestorative agent when employed in a young male rat model of embolic stroke while in an aged model it acts a neuroprotectant. However evaluation of Tβ4 as a treatment of stroke requires further preclinical evaluation in females and in males and females with comorbidities such as, hypertension and diabetes in models of embolic stroke to further define the mechanism of action and potential as a treatment of stroke in humans.

Hallmarks of Aging: An Autophagic Perspective

Autophagy is a major protein turnover pathway by which cellular components are delivered into the lysosomes for degradation and recycling. This intracellular process is able to maintain cellular homeostasis under stress conditions, and its dysregulation could lead to the development of physiological alterations. The autophagic activity has been found to decrease with age, likely contributing to the accumulation of damaged macromolecules and organelles during aging. Interestingly, failure of the autophagic process has been reported to worsen aging-associated diseases, such as neurodegeneration or cancer, among others. Likewise, it has been proposed in different organisms that maintenance of a proper autophagic activity contributes to extending longevity. In this review, we discuss recent papers showing the impact of autophagy on cell activity and age-associated diseases, highlighting the relevance of this process to the hallmarks of aging. Thus, understanding how autophagy plays an important role in aging opens new avenues for the discovery of biochemical and pharmacological targets and the development of novel anti-aging therapeutic approaches.

Clonal-level lineage commitment pathways of hematopoietic stem cells in vivo

While the aggregate differentiation of the hematopoietic stem cell (HSC) population has been extensively studied, little is known about the lineage commitment process of individual HSC clones. Here, we provide lineage commitment maps of HSC clones under homeostasis and after perturbations of the endogenous hematopoietic system. Under homeostasis, all donor-derived HSC clones regenerate blood homogeneously throughout all measured stages and lineages of hematopoiesis. In contrast, after the hematopoietic system has been perturbed by irradiation or by an antagonistic anti-ckit antibody, only a small fraction of donor-derived HSC clones differentiate. Some of these clones dominantly expand and exhibit lineage bias. We identified the cellular origins of clonal dominance and lineage bias and uncovered the lineage commitment pathways that lead HSC clones to different levels of self-renewal and blood production under various transplantation conditions. This study reveals surprising alterations in HSC fate decisions directed by conditioning and identifies the key hematopoiesis stages that may be manipulated to control blood production and balance.

Plausible Links Between Metabolic Networks, Stem Cells, and Longevity

Aging is an inevitable consequence of life, and all multicellular organisms undergo a decline in tissue and organ functions as they age. Several well-known risk factors, such as obesity, diabetes, and lack of physical activity that lead to the cardiovascular system, decline and impede the function of vital organs, ultimately limit overall life span. Over recent years, aging research has experienced an unparalleled growth, particularly with the discovery and recognition of genetic pathways and biochemical processes that control to some extent the rate of aging.In this chapter, we focus on several aspects of stem cell biology and aging, beginning with major cellular hallmarks of aging, endocrine regulation of aging and its impact on stem cell compartment, and mechanisms of increased longevity. We then discuss the role of epigenetic modifications associated with aging and provide an overview on a most recent search of antiaging modalities.

Quantification of somatic mutation flow across individual cell division events by lineage sequencing

Mutation data reveal the dynamic equilibrium between DNA damage and repair processes in cells and are indispensable to the understanding of age-related diseases, tumor evolution, and the acquisition of drug resistance. However, available genome-wide methods have a limited ability to resolve rare somatic variants and the relationships between these variants. Here, we present lineage sequencing, a new genome sequencing approach that enables somatic event reconstruction by providing quality somatic mutation call sets with resolution as high as the single-cell level in subject lineages. Lineage sequencing entails sampling single cells from a population and sequencing subclonal sample sets derived from these cells such that knowledge of relationships among the cells can be used to jointly call variants across the sample set. This approach integrates data from multiple sequence libraries to support each variant and precisely assigns mutations to lineage segments. We applied lineage sequencing to a human colon cancer cell line with a DNA polymerase epsilon (POLE) proofreading deficiency (HT115) and a human retinal epithelial cell line immortalized by constitutive telomerase expression (RPE1). Cells were cultured under continuous observation to link observed single-cell phenotypes with single-cell mutation data. The high sensitivity, specificity, and resolution of the data provide a unique opportunity for quantitative analysis of variation in mutation rate, spectrum, and correlations among variants. Our data show that mutations arrive with nonuniform probability across sublineages and that DNA lesion dynamics may cause strong correlations between certain mutations.

Cooperation of loss of NKX3.1 and inflammation in prostate cancer initiation

Although it is known that inflammation plays a critical role in prostate tumorigenesis, the underlying processes are not well understood. Based on analysis of genetically engineered mouse models combined with correlative analysis of expression profiling data from human prostate tumors, we demonstrate a reciprocal relationship between inflammation and the status of the NKX3.1 homeobox gene associated with prostate cancer initiation. We find that cancer initiation in aged Nkx3.1 mutant mice correlates with enrichment of specific immune populations and increased expression of immunoregulatory genes. Furthermore, expression of these immunoregulatory genes is similarly increased in human prostate tumors having low levels of NKX3.1 expression. We further show that induction of prostatitis in Nkx3.1 mutant mice accelerates prostate cancer initiation, which is coincident with aberrant cellular plasticity and differentiation. Correspondingly, human prostate tumors having low levels of NKX3.1 have de-regulated expression of genes associated with these cellular processes. We propose that loss of function of NKX3.1 accelerates inflammation-driven prostate cancer initiation potentially via aberrant cellular plasticity and impairment of cellular differentiation.This article has an associated First Person interview with the first author of the paper.

LaminA/C regulates epigenetic and chromatin architecture changes upon aging of hematopoietic stem cells

BACKGROUND

The decline of hematopoietic stem cell (HSC) function upon aging contributes to aging-associated immune remodeling and leukemia pathogenesis. Aged HSCs show changes to their epigenome, such as alterations in DNA methylation and histone methylation and acetylation landscapes. We previously showed a correlation between high Cdc42 activity in aged HSCs and the loss of intranuclear epigenetic polarity, or epipolarity, as indicated by the specific distribution of H4K16ac.

RESULTS

Here, we show that not all histone modifications display a polar localization and that a reduction in H4K16ac amount and loss of epipolarity are specific to aged HSCs. Increasing the levels of H4K16ac is not sufficient to restore polarity in aged HSCs and the restoration of HSC function. The changes in H4K16ac upon aging and rejuvenation of HSCs are correlated with a change in chromosome 11 architecture and alterations in nuclear volume and shape. Surprisingly, by taking advantage of knockout mouse models, we demonstrate that increased Cdc42 activity levels correlate with the repression of the nuclear envelope protein LaminA/C, which controls chromosome 11 distribution, H4K16ac polarity, and nuclear volume and shape in aged HSCs.

CONCLUSIONS

Collectively, our data show that chromatin architecture changes in aged stem cells are reversible by decreasing the levels of Cdc42 activity, revealing an unanticipated way to pharmacologically target LaminA/C expression and revert alterations of the epigenetic architecture in aged HSCs.

Mature enteroendocrine cells contribute to basal and pathological stem cell dynamics in the small intestine

Lgr5-expressing intestinal stem cells (ISCs) maintain continuous and rapid generation of the intestinal epithelium. Here, we present evidence that dedifferentiation of committed enteroendocrine cells (EECs) contributes to maintenance of the epithelium under both basal conditions and in response to injury. Lineage-tracing studies identified a subset of EECs that reside at +4 position for more than 2 wk, most of which were BrdU-label-retaining cells. Under basal conditions, cells derived from these EECs grow from the bottom of the crypt to generate intestinal epithelium according to neutral drift kinetics that is consistent with dedifferentiation of mature EECs to ISCs. The lineage tracing of EECs demonstrated reserve stem cell properties in response to radiation-induced injury with the generation of reparative EEC-derived epithelial patches. Finally, the enterochromaffin (EC) cell was the predominant EEC type participating in these stem cell dynamics. These results provide novel insights into the +4 reserve ISC hypothesis, stem cell dynamics of the intestinal epithelium, and in the development of EC-derived small intestinal tumors. NEW & NOTEWORTHY The current manuscript demonstrating that a subset of mature enteroendocrine cells (EECs), predominantly enterochromaffin cells, dedifferentiates to fully functional intestinal stem cells (ISCs) is novel, timely, and important. These cells dedifferentiate to ISCs not only in response to injury but also under basal homeostatic conditions. These novel findings provide a mechanism in which a specified cell can dedifferentiate and contribute to normal tissue plasticity as well as the development of EEC-derived intestinal tumors under pathologic conditions.

Lifespan Kras mutation levels in lung and liver of B6C3F1 mice

Somatic mutations accumulate in the human genome and are correlated with increased cancer incidence as humans age. The standard model for studying the carcinogenic effects of exposures for human risk assessment is the rodent 2-year carcinogenicity assay. However, there is little information regarding the effect of age on cancer-driver gene mutations in these models. The mutant fraction (MF) of Kras codon 12 GGT to GAT and GGT to GTT mutations, oncogenic mutations orthologous between humans and rodents, was quantified over the lifespan of B6C3F1 mice. MFs were measured in lung and liver tissue, organs that frequently develop tumors following carcinogenic exposures. The MFs were evaluated at 4, 6, 8, 12, 21, and 85 weeks, with the 12-week and 21-week time points being coincident with the conclusion of 28-day and 90-day exposure durations used in short-term toxicity testing. The highly sensitive and quantitative Allele-specific Competitive Blocker PCR (ACB-PCR) assay was used to quantify the number of mutant Kras codon 12 alleles. The mouse lung showed a slight, but significant trend increase in the Kras codon 12 GAT mutation over the 85-week period. The trend with age can be equally well-fit by several non-linear functions, but not by a linear function. In contrast, the liver GAT mutation did not increase, and the GTT mutation did not increase for either organ. Even with the slight increase in the lung GAT MFs, our results indicate that the future use of Kras mutation as a biomarker of carcinogenic effect will not be confounded by animal age. Environ. Mol. Mutagen. 59:715-721, 2018. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

Pharmacological Regulation of Oxidative Stress in Stem Cells

Oxidative stress results from an imbalance between reactive oxygen species (ROS) production and antioxidant defense mechanisms. The regulation of stem cell self-renewal and differentiation is crucial for early development and tissue homeostasis. Recent reports have suggested that the balance between self-renewal and differentiation is regulated by the cellular oxidation-reduction (redox) state; therefore, the study of ROS regulation in regenerative medicine has emerged to develop protocols for regulating appropriate stem cell differentiation and maintenance for clinical applications. In this review, we introduce the defined roles of oxidative stress in pluripotent stem cells (PSCs) and hematopoietic stem cells (HSCs) and discuss the potential applications of pharmacological approaches for regulating oxidative stress in regenerative medicine.

Fabrication of Liquid-Crystal-Based Optical Sensing Platform for Detection of Hydrogen Peroxide and Blood Glucose

Rapid and accurate determination of H₂O₂ is of great importance in practical applications. In this study, we demonstrate construction of liquid-crystal (LC)-based sensing platforms for sensitive and real-time detection of H₂O₂ with high accuracy for the first time. Single-stranded DNA (ssDNA) adsorbed onto the surface of nanoceria is released to the aqueous solution in the presence of H₂O₂, which disrupts arrangement of the self-assembled cationic surfactant monolayer decorated at the aqueous/LC interface. Thus, the orientation of LCs changes from a homeotropic to planar state, leading to change in the optical response from dark-to-bright appearance. As H₂O₂ can be produced during oxidation of glucose by glucose oxidase (GOx), detection of glucose is also fulfilled by employing the H₂O₂ sensing platform. Our system can detect H₂O₂ and glucose with concentrations as low as 28.9 nM and 0.52 μM, respectively. It shows high promise of using LC-based sensors for the detection of H₂O₂ and its relevant biomarkers in practical applications.

Metabolism as master of hematopoietic stem cell fate

HSCs have a fate choice when they divide; they can self-renew, producing new HSCs, or produce daughter cells that will mature to become committed cells. Technical challenges, however, have long obscured the mechanics of these choices. Advances in flow-sorting have made possible the purification of HSC populations, but available HSC-enriched fractions still include substantial heterogeneity, and single HSCs have proven extremely difficult to track and observe. Advances in single-cell approaches, however, have led to the identification of a highly purified population of hematopoietic stem cells (HSCs) that make a critical contribution to hematopoietic homeostasis through a preference for self-renewing division. Metabolic cues are key regulators of this cell fate choice, and the importance of controlling the population and quality of mitochondria has recently been highlighted to maintain the equilibrium of HSC populations. Leukemic cells also demand tightly regulated metabolism, and shifting the division balance of leukemic cells toward commitment has been considered as a promising therapeutic strategy. A deeper understanding of precisely how specific modes of metabolism control HSC fate is, therefore, of great biological interest, and more importantly will be critical to the development of new therapeutic strategies that target HSC division balance for the treatment of hematological disease.

The Spectrum of Fundamental Basic Science Discoveries Contributing to Organismal Aging

Aging research has undergone unprecedented advances at an accelerating rate in recent years, leading to excitement in the field as well as opportunities for imagination and innovation. Novel insights indicate that, rather than resulting from a preprogrammed series of events, the aging process is predominantly driven by fundamental non-adaptive mechanisms that are interconnected, linked, and overlap. To varying degrees, these mechanisms also manifest with aging in bone where they cause skeletal fragility. Because these mechanisms of aging can be manipulated, it might be possible to slow, delay, or alleviate multiple age-related diseases and their complications by targeting conserved genetic signaling pathways, controlled functional networks, and basic biochemical processes. Indeed, findings in various mammalian species suggest that targeting fundamental aging mechanisms (eg, via either loss-of-function or gain-of-function mutations or administration of pharmacological therapies) can extend healthspan; ie, the healthy period of life free of chronic diseases. In this review, we summarize the evidence supporting the role of the spectrum of fundamental basic science discoveries contributing to organismal aging, with emphasis on mammalian studies and in particular aging mechanisms in bone that drive skeletal fragility. These mechanisms or aging hallmarks include: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. Because these mechanisms are linked, interventions that ameliorate one hallmark can in theory ameliorate others. In the field of bone and mineral research, current challenges include defining the relative contributions of each aging hallmark to the natural skeletal aging process, better understanding the complex interconnections among the hallmarks, and identifying the most effective therapeutic strategies to safely target multiple hallmarks. Based on their interconnections, it may be feasible to simultaneously interfere with several fundamental aging mechanisms to alleviate a wide spectrum of age-related chronic diseases, including osteoporosis. © 2018 American Society for Bone and Mineral Research.

Nutritional Regulation of Intestinal Stem Cells

Dietary composition and calorie intake are major determinants of health and disease. Calorie restriction promotes metabolic changes that favor tissue regeneration and is arguably the most successful and best-conserved antiaging intervention. Obesity, in contrast, impairs tissue homeostasis and is a major risk factor for the development of diseases including cancer. Stem cells, the central mediators of tissue regeneration, integrate dietary and energy cues via nutrient-sensing pathways to maintain growth or respond to stress. We discuss emerging data on the effects of diet and nutrient-sensing pathways on intestinal stem cells, as well as their potential application in the development of regenerative and therapeutic interventions.

The homeobox transcription factor HB9 induces senescence and blocks differentiation in hematopoietic stem and progenitor cells

The homeobox gene HLXB9 encodes for the transcription factor HB9, which is essential for pancreatic as well as motor neuronal development. Beside its physiological expression pattern, aberrant HB9 expression has been observed in several neoplasias. Especially in infant translocation t(7;12) acute myeloid leukemia, aberrant HB9 expression is the only known molecular hallmark and is assumed to be a key factor in leukemic transformation. However, so far, only poor functional data exist addressing the oncogenic potential of HB9 or its influence on hematopoiesis. We investigated the influence of HB9 on cell proliferation and cell cycle in vitro, as well as on hematopoietic stem cell differentiation in vivo using murine and human model systems. In vitro, HB9 expression led to premature senescence in human HT1080 and murine NIH3T3 cells, providing for the first time evidence for an oncogenic potential of HB9. Onset of senescence was characterized by induction of the p53–p21 tumor suppressor network, resulting in growth arrest, accompanied by morphological transformation and expression of senescence-associated β-galactosidase. In vivo, HB9-transduced primary murine hematopoietic stem and progenitor cells underwent a profound differentiation arrest and accumulated at the megakaryocyte/erythrocyte progenitor stage. In line, gene expression analyses revealed de novo expression of erythropoiesis-related genes in human CD34⁺hematopoietic stem and progenitor cells upon HB9 expression. In summary, the novel findings of HB9-dependent premature senescence and myeloid-biased perturbed hematopoietic differentiation, for the first time shed light on the oncogenic properties of HB9 in translocation t(7;12) acute myeloid leukemia.

Tracing human stem cell lineage during development using DNA methylation

Stem cell maturation is a fundamental, yet poorly understood aspect of human development. We devised a DNA methylation signature deeply reminiscent of embryonic stem cells (a fetal cell origin signature, FCO) to interrogate the evolving character of multiple human tissues. The cell fraction displaying this FCO signature was highly dependent upon developmental stage (fetal versus adult), and in leukocytes, it described a dynamic transition during the first 5 yr of life. Significant individual variation in the FCO signature of leukocytes was evident at birth, in childhood, and throughout adult life. The genes characterizing the signature included transcription factors and proteins intimately involved in embryonic development. We defined and applied a DNA methylation signature common among human fetal hematopoietic progenitor cells and have shown that this signature traces the lineage of cells and informs the study of stem cell heterogeneity in humans under homeostatic conditions.

Integrated computational biology analysis to evaluate target genes for chronic myelogenous leukemia

Although hundreds of genes have been linked to chronic myelogenous leukemia (CML), many of the results lack reproducibility. In the present study, data across multiple modalities were integrated to evaluate 579 CML candidate genes, including literature‑based CML‑gene relation data, Gene Expression Omnibus RNA expression data and pathway‑based gene‑gene interaction data. The expression data included samples from 76 patients with CML and 73 healthy controls. For each target gene, four metrics were proposed and tested with case/control classification. The effectiveness of the four metrics presented was demonstrated by the high classification accuracy (94.63%; P<2x10‑4). Cross metric analysis suggested nine top candidate genes for CML: Epidermal growth factor receptor, tumor protein p53, catenin β 1, janus kinase 2, tumor necrosis factor, abelson murine leukemia viral oncogene homolog 1, vascular endothelial growth factor A, B‑cell lymphoma 2 and proto‑oncogene tyrosine‑protein kinase. In addition, 145 CML candidate pathways enriched with 485 out of 579 genes were identified (P<8.2x10‑11; q=0.005). In conclusion, weighted genetic networks generated using computational biology may be complementary to biological experiments for the evaluation of known or novel CML target genes.

The mitochondrial unfolded protein response is activated upon hematopoietic stem cell exit from quiescence

The mitochondrial unfolded protein response (UPR^mt ), a cellular protective program that ensures proteostasis in the mitochondria, has recently emerged as a regulatory mechanism for adult stem cell maintenance that is conserved across tissues. Despite the emerging genetic evidence implicating the UPR^mt in stem cell maintenance, the underlying molecular mechanism is unknown. While it has been speculated that the UPR^mt is activated upon stem cell transition from quiescence to proliferation, the direct evidence is lacking. In this study, we devised three experimental approaches that enable us to monitor quiescent and proliferating hematopoietic stem cells (HSCs) and provided the direct evidence that the UPR^mt is activated upon HSC transition from quiescence to proliferation, and more broadly, mitochondrial integrity is actively monitored at the restriction point to ensure metabolic fitness before stem cells are committed to proliferation.

Hematopoietic stem cell fate through metabolic control

Hematopoietic stem cells maintain a quiescent state in the bone marrow to preserve their self-renewal capacity, but also undergo cell divisions as required. Organelles such as the mitochondria sustain cumulative damage during these cell divisions and this damage may eventually compromise the cells' self-renewal capacity. Hematopoietic stem cell divisions result in either self-renewal or differentiation, with the balance between the two affecting hematopoietic homeostasis directly; however, the heterogeneity of available hematopoietic stem cell-enriched fractions, together with the technical challenges of observing hematopoietic stem cell behavior, has long hindered the analysis of individual hematopoietic stem cells and prevented the elucidation of this process. Recent advances in genetic models, metabolomics analyses, and single-cell approaches have revealed the contributions made to hematopoietic stem cell self-renewal by metabolic cues, mitochondrial biogenesis, and autophagy/mitophagy, which have highlighted mitochondrial quality control as a key factor in the equilibrium of hematopoietic stem cells. A deeper understanding of precisely how specific modes of metabolism control hematopoietic stem cells fate at the single-cell level is therefore not only of great biological interest, but will also have clear clinical implications for the development of therapies for hematological diseases.

STT3-dependent PD-L1 accumulation on cancer stem cells promotes immune evasion

Enriched PD-L1 expression in cancer stem-like cells (CSCs) contributes to CSC immune evasion. However, the mechanisms underlying PD-L1 enrichment in CSCs remain unclear. Here, we demonstrate that epithelial–mesenchymal transition (EMT) enriches PD-L1 in CSCs by the EMT/β-catenin/STT3/PD-L1 signaling axis, in which EMT transcriptionally induces N-glycosyltransferase STT3 through β-catenin, and subsequent STT3-dependent PD-L1 N-glycosylation stabilizes and upregulates PD-L1. The axis is also utilized by the general cancer cell population, but it has much more profound effect on CSCs as EMT induces more STT3 in CSCs than in non-CSCs. We further identify a non-canonical mesenchymal–epithelial transition (MET) activity of etoposide, which suppresses the EMT/β-catenin/STT3/PD-L1 axis through TOP2B degradation-dependent nuclear β-catenin reduction, leading to PD-L1 downregulation of CSCs and non-CSCs and sensitization of cancer cells to anti-Tim-3 therapy. Together, our results link MET to PD-L1 stabilization through glycosylation regulation and reveal it as a potential strategy to enhance cancer immunotherapy efficacy.

PD-L1 accumulates on cancer stem cells and favours immune evasion but the mechanism underlying this accumulation are unknown. Here the authors show that epithelial-mesenchymal transition induces glycosylation and stabilisation of PD-L1; antagonising this process renders cancer cells sensitive to anti-Tim3-therapy.

DNA damage and tissue repair: What we can learn from planaria

Faithful renewal of aging and damaged tissues is central to organismal lifespan. Stem cells (SCs) generate the cellular progeny that replenish adult tissues across the body but this task becomes increasingly compromised over time. The age related decline in SC-mediated tissue maintenance is a multifactorial event that commonly affects genome integrity. The presence of DNA damage in SCs that are under continuous demand to divide poses a great risk for age-related disorders such as cancer. However, performing analysis of SCs with genomic instability and the DNA damage response during tissue renewal present significant challenges. Here we introduce an alternative experimental system based on the planaria flatworm Schmidtea mediterranea to address at the organismal level studies intersecting SC-mediated tissue renewal in the presence of genomic instability. Planaria have abundant SCs (neoblasts) that maintain high rates of cellular turnover and a variety of molecular tools have been developed to induce DNA damage and dissect how neoblasts respond to this stressor. S. mediterranea displays high evolutionary conservation of DNA repair mechanisms and signaling pathways regulating adult SCs. We describe genetically induced-DNA damage models and highlight body-wide signals affecting cellular decisions such as survival, proliferation, and death in the presence of genomic instability. We also discuss transcriptomic changes in the DNA damage response during injury repair and propose DNA repair as key component of tissue regeneration. Additional studies using planaria will provide insights about mechanisms regulating survival and growth of cells with DNA damage during tissue renewal and regeneration.

A single nanoparticle-based real-time monitoring of biocatalytic progress and detection of hydrogen peroxide

This paper reported a new method to observe the catalytic progress of the natural horseradish peroxidase (HRP) in-situ on single gold nanoparticles (GNPs) by the combination of dark field imaging and plasmonic resonance scattering spectra. The produced single HRP-GNP exhibited localized catalytic property toward H₂O₂-Diaminobenzidine (DAB), which could be used to detect the concentration of H₂O₂ in micro/nanospace. The linear range for H₂O₂ sensing was from 0.01 μM to 5 μM with a detection limit of 10 nM. The new design strategy could be applied for a broader bioanalysis situation by substituting the HRP with other specified biocatalyst.

Cellular responses and gene expression profiles of colonic Lgr5+ stem cells after low-dose/low-dose-rate radiation exposure

We previously found that high-dose-rate radiation induced a replenishment of the colonic Lgr5+ stem cell pool, whereas low-dose-rate radiation did not. To identify key molecules that determine the dose-rate effects on this stem cell pool, we harvested colonic Lgr5+ stem cells by cell sorting at 2 weeks after exposure to 1 Gy of high-dose-rate (30 Gy/h) or low-dose-rate (0.003 Gy/h) radiation and analyzed their gene expression profiles using RNA-Seq. We found that pathways related to DNA damage response, cell growth, cell differentiation and cell death were upregulated in Lgr5+ stem cells irradiated with high dose rates, whereas pathways related to apical junctions and extracellular signaling were upregulated in low-dose-rate-irradiated colonic Lgr5+ stem cells. Interestingly, biological events involving apical junctions are known to play an important role in the exclusion of transformed cells that are surrounded by normal epithelial cells through 'cell competition'. We speculated that cell competition, through apical junctions and extracellular ligands, might contribute to the dose-rate effect on Lgr5+ cell replenishment. To understand this mechanism, we focused on 69 genes that were significantly upregulated in low-dose-rate-irradiated cells, which we named DREDGE (Dose-Rate Effect Determining GEnes). Based on these findings, we propose a possible mechanism underlying the dose-rate effect observed in the colonic stem cell pool.

Djhsp90s are crucial regulators during planarian regeneration and tissue homeostasis

Heat shock protein 90 family members (HSP90s), as molecular chaperones, have conserved roles in the physiological processes of eukaryotes regulating cytoprotection, increasing host resistance and so on. However, whether HSP90s affect regeneration in animals is unclear. Planarians are emerging models for studying regeneration in vivo. Here, the roles of three hsp90 genes from planarian Dugesia japonica are investigated by WISH and RNAi. The results show that: (1) Djhsp90s expressions are induced by heat and cold shock, tissue damage and ionic liquid; (2) Djhsp90s mRNA are mainly distributed each side of the body in intact worms as well as blastemas in regenerative worms; (3) the worms show head regression, lysis, the body curling and the regeneration arrest or even failure after Djhsp90s RNAi; (4) Djhsp90s are involved in autophagy and locomotion of the body. The research results suggest that Djhsp90s are not only conserved in cytoprotection, but also involved in homeostasis maintenance and regeneration process by regulating different pathways in planarians.

Efficient isolation and high yield of epidermal cells from foreskin biopsies by dynamic trypsinization

Cultured keratinocytes play important roles in burn wound healing and scientific research studies. We aimed to modify the isolation method to avoid over-digestion, maximize the number of isolated epidermal cells and establish a more efficient and innocuous way of cell isolation. Compared to the conventional method, the modified method combines the more dynamic process of enzymatic digestion with multiple harvestings of dissociated cells via digestion. The cells from each harvesting were immediately re-suspended in culture medium with serum to avoid extended trypsinization and then pooled for further analysis. The number of viable cells isolated per gram of adult foreskin epidermis was (18.88±13.22)×10⁶ cells in the control group and (67.34±30.66)×10⁶ cells in the modified group (p<0.001). No significant differences were observed in the proportion of CD49f-positive cells between the two groups (p>0.05). The modified method was significantly more efficient in dissociating keratinocytes from each unit of skin biopsy, which is particularly important for treating severe burns when donor skin is limited.

Diminished apoptotic priming and ATM signalling confer a survival advantage onto aged haematopoietic stem cells in response to DNA damage

Ageing of haematopoietic stem cells (HSC) contributes to deficits in the aged haematopoietic system. HSC decline is driven in part by DNA damage accumulation, yet how aging impacts the acute DNA damage response (DDR) of HSCs is poorly understood. We show that old HSCs exhibit diminished ATM activity and attenuated DDR leading to elevated clonal survival in response to a range of genotoxins that was underwritten by diminished apoptotic priming. Distinct HSC subsets exhibited ageing-dependent and subtype-dependent differences in apoptotic priming and survival in response to DNA damage. The defective DDR of old HSCs was non-cell autonomous as ATM signalling, and clonal survival in response to DNA damage could be restored to levels observed in young HSCs post-transplantation into young recipients. These data suggest that defective DDR and diminished apoptotic priming provide a selective advantage to old HSCs that may contribute to mutation accrual and disease predisposition.

Replication stress in hematopoietic stem cells in mouse and man

Life-long blood regeneration relies on a rare population of self-renewing hematopoietic stem cells (HSCs). These cells' nearly unlimited self-renewal potential and lifetime persistence in the body signifies the need for tight control of their genome integrity. Their quiescent state, tightly linked with low metabolic activity, is one of the main strategies employed by HSCs to preserve an intact genome. On the other hand, HSCs need to be able to quickly respond to increased blood demands and rapidly increase their cellular output in order to fight infection-associated inflammation or extensive blood loss. This increase in proliferation rate, however, comes at the price of exposing HSCs to DNA damage inevitably associated with the process of DNA replication. Any interference with normal replication fork progression leads to a specialized molecular response termed replication stress (RS). Importantly, increased levels of RS are a hallmark feature of aged HSCs, where an accumulating body of evidence points to causative relationships between RS and the aging-associated impairment of the blood system's functional capacity. In this review, we present an overview of RS in HSCs focusing on its causes and consequences for the blood system of mice and men.

A matter of life and death: stem cell survival in tissue regeneration and tumour formation

In recent years, great strides have been made in our understanding of how stem cells (SCs) govern tissue homeostasis and regeneration. The inherent longevity of SCs raises the possibility that the unique protective mechanisms in these cells might also be involved in tumorigenesis. In this Opinion article, we discuss how SCs are protected throughout their lifespan, focusing on quiescent behaviour, DNA damage response and programmed cell death. We briefly examine the roles of adult SCs and progenitors in tissue repair and tumorigenesis and explore how signals released from dying or dormant cells influence the function of healthy or aberrant SCs. Important insight into the mechanisms that regulate SC death and survival, as well as the 'legacy' imparted by departing cells, may unlock novel avenues for regenerative medicine and cancer therapy.

An epidemiologic perspective on the stem cell hypothesis in human carcinogenesis

BACKGROUND

Tomasetti and Vogelstein have hypothesized that the patterns of cancer incidence in various cells and tissues are highly correlated with the estimated lifetime number of stem cell divisions. The authors reviewed the risks in tissues of 17 types of cancer from the United States and 69 additional countries. Positive correlations were observed consistently between the tissue - specific cancer incidence and the estimated lifetime number of stem cell divisions. The authors concluded that approximately two-thirds of global cancer incidence may be attributed to random DNA replication errors.

METHODS

An epidemiologic perspective is presented that may serve as a counterpoint in interpreting organ-specific cancer risks. The unifying nature of the Tomasetti/Vogelstein hypothesis must be viewed in the context of diverse and contrasting global trends and patterns of types and "causes" of cancers that are closely linked with economic development and cultural lifestyle practices. The presentation is organized by reviewing the global burden of cancer; concepts of causal inferences and counterfactual assumptions; multifactorial causes of hepatocellular carcinoma and a hierarchy of causes that varies internationally; tobacco carcinogenesis and the multiplex associations with 19 cancer sites and tissues; profile in contrasts in transit through the small and large intestine.

OBSERVATIONS AND CONCLUSIONS

It is readily recognized that DNA replication errors and number of stem cell divisions may vary in individuals and populations due to external environmental genotoxic chemicals and biologic agents, and internal hormonal and metabolic factors. There is a striking contrast in the risk of adenocarcinoma in the small intestine with that in the large intestine. Tomasetti and Vogelstein indicated that the cumulative number of divisions of stem cells over a lifetime in normal epithelial mucosal cells from colorectal cancer patients was 4 time greater than in the epithelial tissue from patients with adenocarcinoma of the small intestine. Their conclusion would suggest a "seed" and "soil" interaction rather than exclusively the independence of either component. Namely, that the contrasting physiological, biochemical, microbial and immunological features in the lumen and on the mucosal surface of the large intestine, in contrast to that in the small intestine, would foster molecular genetic and epigenetic events that are advantageous to neoplasia in the large intestine.

Murine hematopoietic stem cell reconstitution potential is maintained by osteopontin during aging

In adult mammals, hematopoietic stem cells (HSCs) reside in the bone marrow and are in part regulated by the bone marrow microenvironment, called the stem cell niche. We have previously identified the bone marrow morphogen osteopontin (OPN), which is abundantly present in the bone marrow extracellular matrix, as a negative regulator of the size of the HSC pool under physiological conditions. Here, we study the impact of OPN on HSC function during aging using an OPN-knockout mouse model. We show that during aging OPN deficiency is associated with an increase in lymphocytes and a decline in erythrocytes in peripheral blood. In a bone marrow transplantation setting, aged OPN-deficient stem cells show reduced reconstitution ability likely due to insufficient differentiation of HSCs into more mature cells. In serial bone marrow transplantation, aged OPN^−/− bone marrow cells fail to adequately reconstitute red blood cells and platelets, resulting in severe anemia and thrombocytopenia as well as premature deaths of recipient mice. Thus, OPN has different effects on HSCs in aged and young animals and is particularly important to maintain stem cell function in aging mice.

Bcl11a Deficiency Leads to Hematopoietic Stem Cell Defects with an Aging-like Phenotype

B cell CLL/lymphoma 11A (BCL11A) is a transcription factor and regulator of hemoglobin switching that has emerged as a promising therapeutic target for sickle cell disease and thalassemia. In the hematopoietic system, BCL11A is required for B lymphopoiesis, yet its role in other hematopoietic cells, especially hematopoietic stem cells (HSCs) remains elusive. The extensive expression of BCL11A in hematopoiesis implicates context-dependent roles, highlighting the importance of fully characterizing its function as part of ongoing efforts for stem cell therapy and regenerative medicine. Here, we demonstrate that BCL11A is indispensable for normal HSC function. Bcl11a deficiency results in HSC defects, typically observed in the aging hematopoietic system. We find that downregulation of cyclin-dependent kinase 6 (Cdk6), and the ensuing cell-cycle delay, correlate with HSC dysfunction. Our studies define a mechanism for BCL11A in regulation of HSC function and have important implications for the design of therapeutic approaches to targeting BCL11A.

MZF-1/Elk-1 interaction domain as therapeutic target for protein kinase Cα-based triple-negative breast cancer cells

Recent reports demonstrate that the expression of protein kinase C alpha (PKCα) in triple-negative breast cancer (TNBC) correlates with decreased survival outcomes. However, off-target effects of targeting PKCα and limited understanding of the signaling mechanisms upstream of PKCα have hampered previous efforts to manipulate this ubiquitous gene. This study shows that the expression of both myeloid zinc finger 1 (MZF-1) and Ets-like protein-1 (Elk-1) correlates with PKCα expression in TNBC. We found that the acidic domain of MZF-1 and the heparin-binding domain of Elk-1 facilitate the heterodimeric interaction between the two genes before the complex formation binds to the PKCα promoter. Blocking the formation of the heterodimer by transfection of MZF-160-72 or Elk-1145-157 peptide fragments at the MZF-1 / Elk-1 interface decreases DNA-binding activity of the MZF-1 / Elk-1 complex at the PKCα promoter. Subsequently, PKCα expression, migration, tumorigenicity, and the epithelial-mesenchymal transition potential of TNBC cells decrease. These subsequent effects are reversed by transfection with full-length PKCα, confirming that the MZF-1/Elk-1 heterodimer is a mediator of PKCα in TNBC cells. These data suggest that the next therapeutic strategy in treating PKCα-related cancer will be developed from blocking MZF-1/Elk-1 interaction through their binding domain.

EZH2 promotes colorectal cancer stem-like cell expansion by activating p21cip1-Wnt/β-catenin signaling

Because colorectal cancer (CRC) stem-like cells (CCS-like cells) contribute to poor patient prognosis, these cells are a potential target for CRC therapy. However, the mechanism underlying the maintenance of CCS-like cell properties remains unclear. Here, we found that patients with advanced stage CRC expressed high levels of polycomb group protein enhancer of zeste homologue 2 (EZH2). High expression of EZH2 in tumor tissues correlated with poor patient prognosis. Conversely, silencing EZH2 reduced CRC cell proliferation. Surprisingly, EZH2 was more highly expressed in the CCS-like cell subpopulation than in the non-CCS-like cell subpopulation. EZH2 knockdown significantly reduced the CD133⁺/CD44⁺ subpopulation, suppressed mammosphere formation, and decreased the expression of self-renewal-related genes and strongly impaired tumor-initiating capacity in a re-implantation mouse model. Gene expression data from 433 human CRC specimens from TCGA database and in vitro results revealed that EZH2 helped maintain CCS-like cell properties by activating the Wnt/β-catenin pathway. We further revealed that p21^cip1–mediated arrest of the cell cycle at G1/S phase is required for EZH2 activation of the Wnt/β-catenin pathway. Moreover, the specific EZH2 inhibitor EPZ-6438, a clinical trial drug, prevented CRC progression. Collectively, these findings revealed EZH2 maintaining CCS-like cell characteristics by arresting the cell cycle at the G1/S phase. These results indicate a new approach to CRC therapy.

Aging of Human Adult Stem Cells

With the continuous development of stem cell research in recent years, it is realized that stem cell aging may be the core issue of organ aging. As an important approach and main content of regenerative medicine, the stem cell research brings great hope to overcome difficult diseases and improve the quality of life for human beings and become the key to solve this issue. Based on this research, the varying characteristics of stem cells in aging could be recognized; the role of stem cells in the organ aging and regeneration will be revealed; the function of stem cells will be controllable and regulatable in tissues and organs; the stem cells from tissues and organs with rapid or slow cell renewal (e.g., liver and neuron) could be continuously observed from the levels of cellular molecules and dynamic complex. With the assistance of systematical research approaches, the function and mechanism studies can be conducted via multi-perspectives and levels during the different stages of organ aging and regeneration. All of the abovementioned requires great efforts to thoroughly understand the basic rule and the way of stem cell regulation in organ aging and regeneration. Final to the end, the dream of antiaging, efficient repair, and organ remodeling could be realized and also can meet the major needs of population health and disease treatment in our country, meaningfully to contribute benefits for the health of human beings.