251
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PDGF signalling controls age-dependent proliferation in pancreatic β-cells. Nature 2011; 478:349-55. [PMID: 21993628 DOI: 10.1038/nature10502] [Citation(s) in RCA: 212] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2011] [Accepted: 08/24/2011] [Indexed: 12/29/2022]
Abstract
Determining the signalling pathways that direct tissue expansion is a principal goal of regenerative biology. Vigorous pancreatic β-cell replication in juvenile mice and humans declines with age, and elucidating the basis for this decay may reveal strategies for inducing β-cell expansion, a long-sought goal for diabetes therapy. Here we show that platelet-derived growth factor receptor (Pdgfr) signalling controls age-dependent β-cell proliferation in mouse and human pancreatic islets. With age, declining β-cell Pdgfr levels were accompanied by reductions in β-cell enhancer of zeste homologue 2 (Ezh2) levels and β-cell replication. Conditional inactivation of the Pdgfra gene in β-cells accelerated these changes, preventing mouse neonatal β-cell expansion and adult β-cell regeneration. Targeted human PDGFR-α activation in mouse β-cells stimulated Erk1/2 phosphorylation, leading to Ezh2-dependent expansion of adult β-cells. Adult human islets lack PDGF signalling competence, but exposure of juvenile human islets to PDGF-AA stimulated β-cell proliferation. The discovery of a conserved pathway controlling age-dependent β-cell proliferation indicates new strategies for β-cell expansion.
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252
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Tschen SI, Georgia S, Dhawan S, Bhushan A. Skp2 is required for incretin hormone-mediated β-cell proliferation. Mol Endocrinol 2011; 25:2134-43. [PMID: 21980072 DOI: 10.1210/me.2011-1119] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The glucoincretin hormone glucagon-like peptide-1 (GLP-1) and its analog exendin-4 (Ex-4) promote β-cell growth and expansion. Here we report an essential role for Skp2, a substrate recognition component of SCF (Skp, Cullin, F-box) ubiquitin ligase, in promoting glucoincretin-induced β-cell proliferation by regulating the cellular abundance of p27. In vitro, GLP-1 treatment increases Skp2 levels, which accelerates p27 degradation, whereas in vivo, loss of Skp2 prevents glucoincretin-induced β-cell proliferation. Using inhibitors of phosphatidylinositol 3-kinase and Irs2 silencing RNA, we also show that the effects of GLP-1 in facilitating Skp2-dependent p27 degradation are mediated via the Irs2-phosphatidylinositol-3 kinase pathway. Finally, we show that down-regulation of p27 occurs in islets from aged mice and humans, although in these islets, age-dependent accumulation of p16(Ink4a) prevent glucoincretin-induced β-cell proliferation; however, ductal cell proliferation is maintained. Taken together, these data highlight a critical role for Skp2 in glucoincretin-induced β-cell proliferation.
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Affiliation(s)
- Shuen-Ing Tschen
- Department of Medicine, University of California, Los Angeles, Los Angeles, California 90095-7073, USA
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253
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Singh GB, Sharma R, Khullar M. Epigenetics and diabetic cardiomyopathy. Diabetes Res Clin Pract 2011; 94:14-21. [PMID: 21696841 DOI: 10.1016/j.diabres.2011.05.033] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Revised: 05/19/2011] [Accepted: 05/23/2011] [Indexed: 01/21/2023]
Abstract
Cardiovascular complications are a chief cause of mortality and morbidity in diabetic patients. Recent studies suggest that epigenetic changes which may arise as a consequence of environmental factors play an important role in predisposition to disease. Epigenetic mechanisms such as DNA methylation, chromatin remodeling and histone modifications regulate the gene expression in response to environmental signals. Role of epigenetics has been recognized in the pathology of diabetes, however its role in diabetic associated cardiomyopathy remains largely unexplored. In this article, we review current literature on the epigenetic mechanisms involved in diabetes and discuss recent evidence of epigenetic changes that may play an important role in pathophysiology of DCM.
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Affiliation(s)
- Gurinder Bir Singh
- Department of Experimental Medicine and Biotechnology, Post Graduate Institute of Medical Education and Research, Chandigarh, India
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254
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Schaffer AE, Yang AJ, Thorel F, Herrera PL, Sander M. Transgenic overexpression of the transcription factor Nkx6.1 in β-cells of mice does not increase β-cell proliferation, β-cell mass, or improve glucose clearance. Mol Endocrinol 2011; 25:1904-14. [PMID: 21964593 DOI: 10.1210/me.2011-1010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The loss or dysfunction of the pancreatic endocrine β-cell results in diabetes. Recent innovative therapeutic approaches for diabetes aim to induce β-cell proliferation in vivo by pharmacological intervention. Based on the finding that overexpression of the transcription factor Nkx6.1 in islets in vitro increases β-cell proliferation while maintaining β-cell function, Nkx6.1 has been proposed as a potential target for diabetes therapy. However, it is unknown whether elevated Nkx6.1 levels in β-cells in vivo have similar effects as observed in isolated islets. To this end, we sought to investigate whether overexpression of Nkx6.1 in β-cells in vivo could increase β-cell mass and/or improve β-cell function in normal or β-cell-depleted mice. Using a bigenic inducible Cre-recombinase-based transgenic model, we analyzed the effects of Nkx6.1 overexpression on β-cell proliferation, β-cell mass, and glucose metabolism. We found that mice overexpressing Nkx6.1 in β-cells displayed similar β-cell proliferation rates and β-cell mass as control mice. Furthermore, after partial β-cell ablation, Nkx6.1 overexpression was not sufficient to induce β-cell regeneration under either nondiabetic or diabetic conditions. Together these results demonstrate that sustained Nkx6.1 overexpression in vivo does not stimulate β-cell proliferation, expand β-cell mass, or improve glucose metabolism in either normal or β-cell-depleted pancreata. Thus, raising cellular Nkx6.1 levels in β-cells in vivo is unlikely to have a positive impact on type 2 diabetes.
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Affiliation(s)
- Ashleigh E Schaffer
- Department of Cellular and Molecular Medicine, The University of California, San Diego, USA.
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255
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Abstract
INTRODUCTION The revolution of epigenetics has revitalized cancer research, shifting focus away from somatic mutation toward a more holistic perspective involving the dynamic states of chromatin. Disruption of chromatin organization can directly and indirectly precipitate genomic instability and transformation. DISCUSSION One group of epigenetic mediators, the Polycomb group (PcG) proteins, establishes heritable gene repression through methylation of histone tails. Although classically considered regulators of development and cellular differentiation, PcG proteins engage in a variety of neoplastic processes, including cellular proliferation and invasion. Due to their multifaceted potential, PcG proteins rest at the intersection of transcriptional memory and malignancy. Expression levels of PcG proteins hold enormous diagnostic and prognostic value in breast, prostate, and more recently, gastrointestinal cancers. CONCLUSION In this review, we briefly summarize the function of PcG proteins and report the latest developments in understanding their role in pancreatic cancer.
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256
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Chen C, Zhao M, Yin N, He B, Wang B, Yuan Y, Yu F, Hu J, Yin B, Lu Q. Abnormal histone acetylation and methylation levels in esophageal squamous cell carcinomas. Cancer Invest 2011; 29:548-56. [PMID: 21843048 DOI: 10.3109/07357907.2011.597810] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
To investigate whether alterations in histone modifications occur in esophageal squamous cell carcinoma (ESCC), we measured histone H3/ H4 acetylation and H3K4/H3K27 methylation levels, as well as the expression of chromatin modifier genes in tumor and healthy esophageal tissue from ESCC patients. We found evidence of global H3 and H4 hypoacetylation, H3K4 and H3K27 hypermethylation in ESCC tissue. Both H3 hypoacetylation and H3K27 hypermethylation correlated with the severity and histological differentiation of the tumor, and H3K4 hypermethylation also correlated with tumor differentiation. Our results suggest that aberrant histone modifications may play an important role in the development and progression of ESCC.
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Affiliation(s)
- Chen Chen
- Department of Cardiothoracic Surgery, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
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257
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Jarid2 regulates mouse epidermal stem cell activation and differentiation. EMBO J 2011; 30:3635-46. [PMID: 21811233 DOI: 10.1038/emboj.2011.265] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2011] [Accepted: 07/08/2011] [Indexed: 12/17/2022] Open
Abstract
Jarid2 is required for the genomic recruitment of the polycomb repressive complex-2 (PRC2) in embryonic stem cells. However, its specific role during late development and adult tissues remains largely uncharacterized. Here, we show that deletion of Jarid2 in mouse epidermis reduces the proliferation and potentiates the differentiation of postnatal epidermal progenitors, without affecting epidermal development. In neonatal epidermis, Jarid2 deficiency reduces H3K27 trimethylation, a chromatin repressive mark, in epidermal differentiation genes previously shown to be targets of the PRC2. However, in adult epidermis Jarid2 depletion does not affect interfollicular epidermal differentiation but results in delayed hair follicle (HF) cycling as a consequence of decreased proliferation of HF stem cells and their progeny. We conclude that Jarid2 is required for the scheduled proliferation of epidermal stem and progenitor cells necessary to maintain epidermal homeostasis.
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258
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Wyngaarden LA, Delgado-Olguin P, Su IH, Bruneau BG, Hopyan S. Ezh2 regulates anteroposterior axis specification and proximodistal axis elongation in the developing limb. Development 2011; 138:3759-67. [PMID: 21795281 DOI: 10.1242/dev.063180] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Specification and determination (commitment) of positional identities precedes overt pattern formation during development. In the limb bud, it is clear that the anteroposterior axis is specified at a very early stage and is prepatterned by the mutually antagonistic interaction between Gli3 and Hand2. There is also evidence that the proximodistal axis is specified early and determined progressively. Little is known about upstream regulators of these processes or how epigenetic modifiers influence axis formation. Using conditional mutagenesis at different time points, we show that the histone methyltransferase Ezh2 is an upstream regulator of anteroposterior prepattern at an early stage. Mutants exhibit posteriorised limb bud identity. During later limb bud stages, Ezh2 is essential for cell survival and proximodistal segment elongation. Ezh2 maintains the late phase of Hox gene expression and cell transposition experiments suggest that it regulates the plasticity with which cells respond to instructive positional cues.
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Affiliation(s)
- Laurie A Wyngaarden
- Developmental and Stem Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, ON M5G 1X8, Canada
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259
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Polycomb EZH2 controls self-renewal and safeguards the transcriptional identity of skeletal muscle stem cells. Genes Dev 2011; 25:789-94. [PMID: 21498568 DOI: 10.1101/gad.2027911] [Citation(s) in RCA: 168] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Satellite cells (SCs) sustain muscle growth and empower adult skeletal muscle with vigorous regenerative abilities. Here, we report that EZH2, the enzymatic subunit of the Polycomb-repressive complex 2 (PRC2), is expressed in both Pax7+/Myf5⁻ stem cells and Pax7+/Myf5+ committed myogenic precursors and is required for homeostasis of the adult SC pool. Mice with conditional ablation of Ezh2 in SCs have fewer muscle postnatal Pax7+ cells and reduced muscle mass and fail to appropriately regenerate. These defects are associated with impaired SC proliferation and derepression of genes expressed in nonmuscle cell lineages. Thus, EZH2 controls self-renewal and proliferation, and maintains an appropriate transcriptional program in SCs.
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260
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Atkinson MA, Bluestone JA, Eisenbarth GS, Hebrok M, Herold KC, Accili D, Pietropaolo M, Arvan PR, Von Herrath M, Markel DS, Rhodes CJ. How does type 1 diabetes develop?: the notion of homicide or β-cell suicide revisited. Diabetes 2011; 60:1370-9. [PMID: 21525508 PMCID: PMC3292309 DOI: 10.2337/db10-1797] [Citation(s) in RCA: 167] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/29/2010] [Accepted: 02/17/2011] [Indexed: 12/16/2022]
Affiliation(s)
- Mark A Atkinson
- Department of Pediatrics, University of Florida, Gainesville, Florida, USA.
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261
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Hinault C, Kawamori D, Liew CW, Maier B, Hu J, Keller SR, Mirmira RG, Scrable H, Kulkarni RN. Δ40 Isoform of p53 controls β-cell proliferation and glucose homeostasis in mice. Diabetes 2011; 60:1210-22. [PMID: 21357466 PMCID: PMC3064094 DOI: 10.2337/db09-1379] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
OBJECTIVE Investigating the dynamics of pancreatic β-cell mass is critical for developing strategies to treat both type 1 and type 2 diabetes. p53, a key regulator of the cell cycle and apoptosis, has mostly been a focus of investigation as a tumor suppressor. Although p53 alternative transcripts can modulate p53 activity, their functions are not fully understood. We hypothesized that β-cell proliferation and glucose homeostasis were controlled by Δ40p53, a p53 isoform lacking the transactivation domain of the full-length protein that modulates total p53 activity and regulates organ size and life span in mice. RESEARCH DESIGN AND METHODS We phenotyped metabolic parameters in Δ40p53 transgenic (p44tg) mice and used quantitative RT-PCR, Western blotting, and immunohistochemistry to examine β-cell proliferation. RESULTS Transgenic mice with an ectopic p53 gene encoding Δ40p53 developed hypoinsulinemia and glucose intolerance by 3 months of age, which worsened in older mice and led to overt diabetes and premature death from ∼14 months of age. Consistent with a dramatic decrease in β-cell mass and reduced β-cell proliferation, lower expression of cyclin D2 and pancreatic duodenal homeobox-1, two key regulators of proliferation, was observed, whereas expression of the cell cycle inhibitor p21, a p53 target gene, was increased. CONCLUSIONS These data indicate a significant and novel role for Δ40p53 in β-cell proliferation with implications for the development of age-dependent diabetes.
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Affiliation(s)
- Charlotte Hinault
- Research Division, Joslin Diabetes Center and Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
| | - Dan Kawamori
- Research Division, Joslin Diabetes Center and Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
| | - Chong Wee Liew
- Research Division, Joslin Diabetes Center and Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
| | - Bernhard Maier
- Wells Center for Pediatric Research, Department of Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana
| | - Jiang Hu
- Research Division, Joslin Diabetes Center and Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
| | | | - Raghavendra G. Mirmira
- Wells Center for Pediatric Research, Department of Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana
| | - Heidi Scrable
- Kogod Center on Aging, Mayo Clinic, Rochester, Minnesota
| | - Rohit N. Kulkarni
- Research Division, Joslin Diabetes Center and Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
- Corresponding author: Rohit N. Kulkarni,
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262
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Sandovici I, Smith NH, Nitert MD, Ackers-Johnson M, Uribe-Lewis S, Ito Y, Jones RH, Marquez VE, Cairns W, Tadayyon M, O’Neill LP, Murrell A, Ling C, Constância M, Ozanne SE. Maternal diet and aging alter the epigenetic control of a promoter-enhancer interaction at the Hnf4a gene in rat pancreatic islets. Proc Natl Acad Sci U S A 2011; 108:5449-54. [PMID: 21385945 PMCID: PMC3069181 DOI: 10.1073/pnas.1019007108] [Citation(s) in RCA: 235] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Environmental factors interact with the genome throughout life to determine gene expression and, consequently, tissue function and disease risk. One such factor that is known to play an important role in determining long-term metabolic health is diet during critical periods of development. Epigenetic regulation of gene expression has been implicated in mediating these programming effects of early diet. The precise epigenetic mechanisms that underlie these effects remain largely unknown. Here, we show that the transcription factor Hnf4a, which has been implicated in the etiology of type 2 diabetes (T2D), is epigenetically regulated by maternal diet and aging in rat islets. Transcriptional activity of Hnf4a in islets is restricted to the distal P2 promoter through its open chromatin configuration and an islet-specific interaction between the P2 promoter and a downstream enhancer. Exposure to suboptimal nutrition during early development leads to epigenetic silencing at the enhancer region, which weakens the P2 promoter-enhancer interaction and results in a permanent reduction in Hnf4a expression. Aging leads to progressive epigenetic silencing of the entire Hnf4a locus in islets, an effect that is more pronounced in rats exposed to a poor maternal diet. Our findings provide evidence for environmentally induced epigenetic changes at the Hnf4a enhancer that alter its interaction with the P2 promoter, and consequently determine T2D risk. We therefore propose that environmentally induced changes in promoter-enhancer interactions represent a fundamental epigenetic mechanism by which nutrition and aging can influence long-term health.
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Affiliation(s)
- Ionel Sandovici
- Metabolic Research Laboratories, Department of Obstetrics and Gynaecology, University of Cambridge, Cambridge CB2 0SW, United Kingdom
- Centre for Trophoblast Research, University of Cambridge, Cambridge CB2 3EG, United Kingdom
| | - Noel H. Smith
- Metabolic Research Laboratories, Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, United Kingdom
| | - Marloes Dekker Nitert
- Diabetes and Endocrinology Research Unit, Lund University, Malmö University Hospital, S-205 02 Malmö, Sweden
| | - Matthew Ackers-Johnson
- Metabolic Research Laboratories, Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, United Kingdom
| | - Santiago Uribe-Lewis
- Cancer Research United Kingdom Cambridge Research Institute, Department of Oncology, University of Cambridge, Cambridge CB2 0RE, United Kingdom
| | - Yoko Ito
- Cancer Research United Kingdom Cambridge Research Institute, Department of Oncology, University of Cambridge, Cambridge CB2 0RE, United Kingdom
| | - R. Huw Jones
- Metabolic Research Laboratories, Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, United Kingdom
| | - Victor E. Marquez
- Chemical Biology Laboratory, Center for Cancer Research, National Cancer Institute at Frederick, National Institutes of Health, Frederick, MD 21702
| | - William Cairns
- Biological Reagents and Assay Development, Medicines Research Centre, GlaxoSmithKline, Stevenage SG1 2NY, United Kingdom; and
| | - Mohammed Tadayyon
- Biological Reagents and Assay Development, Medicines Research Centre, GlaxoSmithKline, Stevenage SG1 2NY, United Kingdom; and
| | - Laura P. O’Neill
- Chromatin and Gene Expression Group, Institute of Biomedical Research, University of Birmingham Medical School, Birmingham B15 2TT, United Kingdom
| | - Adele Murrell
- Cancer Research United Kingdom Cambridge Research Institute, Department of Oncology, University of Cambridge, Cambridge CB2 0RE, United Kingdom
| | - Charlotte Ling
- Diabetes and Endocrinology Research Unit, Lund University, Malmö University Hospital, S-205 02 Malmö, Sweden
| | - Miguel Constância
- Metabolic Research Laboratories, Department of Obstetrics and Gynaecology, University of Cambridge, Cambridge CB2 0SW, United Kingdom
- Centre for Trophoblast Research, University of Cambridge, Cambridge CB2 3EG, United Kingdom
| | - Susan E. Ozanne
- Metabolic Research Laboratories, Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, United Kingdom
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263
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Lee SH, Itkin-Ansari P, Levine F. CENP-A, a protein required for chromosome segregation in mitosis, declines with age in islet but not exocrine cells. Aging (Albany NY) 2011; 2:785-90. [PMID: 21068465 PMCID: PMC3006021 DOI: 10.18632/aging.100220] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Beta-cell replication dramatically declines with age. Here, we report that the level of CENP-A, a protein required for cell division, declines precipitously with age in an islet-specific manner. CENP-A is essentially undetectable after age 29 in humans. However, exocrine cells retain CENP-A expression. The decline in islet-cell CENP-A expression is more striking in humans than in mice, where CENP-A expression continues to be detectable at low levels even in elderly mice. The mechanism by which CENP-A declines appears to be post-transcriptional, as there was no correlation between CENP-A mRNA levels and age or islet purity. This finding has implications for efforts to induce beta-cell replication as a treatment for diabetes.
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Affiliation(s)
- Seung-Hee Lee
- Sanford Children's Health Research Center, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA
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264
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Kong Y, Cui H, Ramkumar C, Zhang H. Regulation of senescence in cancer and aging. J Aging Res 2011; 2011:963172. [PMID: 21423549 PMCID: PMC3056284 DOI: 10.4061/2011/963172] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2010] [Accepted: 01/12/2011] [Indexed: 12/12/2022] Open
Abstract
Senescence is regarded as a physiological response of cells to stress, including telomere dysfunction, aberrant oncogenic activation, DNA damage, and oxidative stress. This stress response has an antagonistically pleiotropic effect to organisms: beneficial as a tumor suppressor, but detrimental by contributing to aging. The emergence of senescence as an effective tumor suppression mechanism is highlighted by recent demonstration that senescence prevents proliferation of cells at risk of neoplastic transformation. Consequently, induction of senescence is recognized as a potential treatment of cancer. Substantial evidence also suggests that senescence plays an important role in aging, particularly in aging of stem cells. In this paper, we will discuss the molecular regulation of senescence its role in cancer and aging. The potential utility of senescence in cancer therapeutics will also be discussed.
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Affiliation(s)
- Yahui Kong
- Department of Cell Biology, University of Massachusetts Medical School, 55 Lake Avenue North, S7-125, Worcester, MA 01655, USA
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265
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Lanigan F, Geraghty JG, Bracken AP. Transcriptional regulation of cellular senescence. Oncogene 2011; 30:2901-11. [PMID: 21383691 DOI: 10.1038/onc.2011.34] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Cellular senescence is an irreversible arrest of proliferation. It is activated when a cell encounters stress such as DNA damage, telomere shortening or oncogene activation. Like apoptosis, it impedes tumour progression and acts as a barrier that pre-neoplastic cells must overcome during their evolution toward the full tumourigenic state. This review focuses on the role of transcriptional regulators in the control of cellular senescence, explores how their function is perturbed in cancer and discusses the potential to harness this knowledge for future cancer therapies.
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Affiliation(s)
- F Lanigan
- Smurfit Genetics Department, The Smurfit Institute of Genetics, Trinity College Dublin, Dublin, Ireland
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266
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EZH1 and EZH2 cogovern histone H3K27 trimethylation and are essential for hair follicle homeostasis and wound repair. Genes Dev 2011; 25:485-98. [PMID: 21317239 DOI: 10.1101/gad.2019811] [Citation(s) in RCA: 292] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Polycomb protein group (PcG)-dependent trimethylation on H3K27 (H3K27me3) regulates identity of embryonic stem cells (ESCs). How H3K27me3 governs adult SCs and tissue development is unclear. Here, we conditionally target H3K27 methyltransferases Ezh2 and Ezh1 to address their roles in mouse skin homeostasis. Postnatal phenotypes appear only in doubly targeted skin, where H3K27me3 is abolished, revealing functional redundancy in EZH1/2 proteins. Surprisingly, while Ezh1/2-null hair follicles (HFs) arrest morphogenesis and degenerate due to defective proliferation and increased apoptosis, epidermis hyperproliferates and survives engraftment. mRNA microarray studies reveal that, despite these striking phenotypic differences, similar genes are up-regulated in HF and epidermal Ezh1/2-null progenitors. Featured prominently are (1) PcG-controlled nonskin lineage genes, whose expression is still significantly lower than in native tissues, and (2) the PcG-regulated Ink4a/Inkb/Arf locus. Interestingly, when EZH1/2 are absent, even though Ink4a/Arf/Ink4b genes are fully activated in HF cells, they are only partially so in epidermal progenitors. Importantly, transduction of Ink4b/Ink4a/Arf shRNAs restores proliferation/survival of Ezh1/2-null HF progenitors in vitro, pointing toward the relevance of this locus to the observed HF phenotypes. Our findings reveal new insights into Polycomb-dependent tissue control, and provide a new twist to how different progenitors within one tissue respond to loss of H3K27me3.
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267
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Abstract
Previous authors have suggested that tumor suppressor expression promotes aging while preventing cancer, but direct experimental support for this cancer-aging hypothesis has been elusive. Here, by using somatic, tissue-specific inactivation of the p16(INK4a) tumor suppressor in murine T- or B-lymphoid progenitors, we report that ablation of p16(INK4a) can either rescue aging or promote cancer in a lineage-specific manner. Deletion of p16(INK4a) in the T lineage ameliorated several aging phenotypes, including thymic involution, decreased production of naive T cells, reduction in homeostatic T-cell proliferation, and attenuation of antigen-specific immune responses. Increased T-cell neoplasia was not observed with somatic p16(INK4a) inactivation in T cells. In contrast, B lineage-specific ablation of p16(INK4a) was associated with a markedly increased incidence of systemic, high-grade B-cell neoplasms, which limited studies of the effects of somatic p16(INK4a) ablation on B-cell aging. Together, these data show that expression of p16(INK4a) can promote aging and prevent cancer in related lymphoid progeny of a common stem cell.
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268
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Interaction of SET domains with histones and nucleic acid structures in active chromatin. Clin Epigenetics 2011; 2:17-25. [PMID: 22704267 PMCID: PMC3365373 DOI: 10.1007/s13148-010-0015-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2010] [Accepted: 11/16/2010] [Indexed: 12/28/2022] Open
Abstract
Changes in the normal program of gene expression are the basis for a number of human diseases. Epigenetic control of gene expression is programmed by chromatin modifications—the inheritable “histone code”—the major component of which is histone methylation. This chromatin methylation code of gene activity is created upon cell differentiation and is further controlled by the “SET” (methyltransferase) domain proteins which maintain this histone methylation pattern and preserve it through rounds of cell division. The molecular principles of epigenetic gene maintenance are essential for proper treatment and prevention of disorders and their complications. However, the principles of epigenetic gene programming are not resolved. Here we discuss some evidence of how the SET proteins determine the required states of target genes and maintain the required levels of their activity. We suggest that, along with other recognition pathways, SET domains can directly recognize the nucleosome and nucleic acids intermediates that are specific for active chromatin regions.
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269
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Köhler CU, Olewinski M, Tannapfel A, Schmidt WE, Fritsch H, Meier JJ. Cell cycle control of β-cell replication in the prenatal and postnatal human pancreas. Am J Physiol Endocrinol Metab 2011; 300:E221-30. [PMID: 20978233 DOI: 10.1152/ajpendo.00496.2010] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
β-Cell regeneration declines with aging, but the molecular mechanisms controlling β-cell replication in humans are not well understood. We compared the expression of selected cell cycle proteins in prenatal and adult tissue and examined the association of these proteins with β-cell replication. Pancreatic tissue from a total of 20 human fetuses and adults was stained for Ki67, cyclin D3, p16 and p27, and insulin. The β-cellular expression of these cell cycle proteins was determined. The frequency of β-cell replication was lower in adult compared with prenatal β-cells (<0.5 vs. 3.4 ± 0.5%, respectively; P < 0.0001). p16 was sporadically expressed in prenatal β-cells (8.0 ± 1.1%) but highly enriched in adult β-cells (63.1 ± 5.2%, P < 0.0001). Likewise, the expression of p27 was much lower in prenatal β-cells (1.7 ± 0.4 vs. 44.1 ± 5.4%, respectively, P < 0.0001), and cyclin D3 expression increased from 24.2 ± 4.1 to 47.25 ± 5.0%, respectively (P < 0.001), with aging. The expression of all three proteins was significantly correlated with each other (P < 0.01 and r > 0.75, respectively). The strong expression of cyclin D3 in adult human β-cells and its correlation to p27 and p16 suggest a positive role in human β-cell cycle regulation. p16 and p27 appear to restrict β-cell replication with aging. The age dependency of cell cycle regulation in human β-cells might explain the reduced β-cell regeneration in adult humans.
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Affiliation(s)
- Christina U Köhler
- Department of Medicine I, St. Josef-Hospital, Ruhr-University of Bochum, Gudrunstr. 56, 44791 Bochum, Germany
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270
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Burd CE, Jeck WR, Liu Y, Sanoff HK, Wang Z, Sharpless NE. Expression of linear and novel circular forms of an INK4/ARF-associated non-coding RNA correlates with atherosclerosis risk. PLoS Genet 2010; 6:e1001233. [PMID: 21151960 PMCID: PMC2996334 DOI: 10.1371/journal.pgen.1001233] [Citation(s) in RCA: 709] [Impact Index Per Article: 50.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2010] [Accepted: 11/02/2010] [Indexed: 12/02/2022] Open
Abstract
Human genome-wide association studies have linked single nucleotide polymorphisms (SNPs) on chromosome 9p21.3 near the INK4/ARF (CDKN2a/b) locus with susceptibility to atherosclerotic vascular disease (ASVD). Although this locus encodes three well-characterized tumor suppressors, p16INK4a, p15INK4b, and ARF, the SNPs most strongly associated with ASVD are ∼120 kb from the nearest coding gene within a long non-coding RNA (ncRNA) known as ANRIL (CDKN2BAS). While individuals homozygous for the atherosclerotic risk allele show decreased expression of ANRIL and the coding INK4/ARF transcripts, the mechanism by which such distant genetic variants influence INK4/ARF expression is unknown. Here, using rapid amplification of cDNA ends (RACE) and analysis of next-generation RNA sequencing datasets, we determined the structure and abundance of multiple ANRIL species. Each of these species was present at very low copy numbers in primary and cultured cells; however, only the expression of ANRIL isoforms containing exons proximal to the INK4/ARF locus correlated with the ASVD risk alleles. Surprisingly, RACE also identified transcripts containing non-colinear ANRIL exonic sequences, whose expression also correlated with genotype and INK4/ARF expression. These non-polyadenylated RNAs resisted RNAse R digestion and could be PCR amplified using outward-facing primers, suggesting they represent circular RNA structures that could arise from by-products of mRNA splicing. Next-generation DNA sequencing and splice prediction algorithms identified polymorphisms within the ASVD risk interval that may regulate ANRIL splicing and circular ANRIL (cANRIL) production. These results identify novel circular RNA products emanating from the ANRIL locus and suggest causal variants at 9p21.3 regulate INK4/ARF expression and ASVD risk by modulating ANRIL expression and/or structure. Unbiased studies of the human genome have identified strong genetic determinants of atherosclerotic vascular disease (ASVD) on chromosome 9p21.3. This region of the genome does not encode genes previously linked to ASVD, but does contain the INK4/ARF tumor suppressor locus. Products of the INK4/ARF locus regulate cell division, a process thought to be important in ASVD pathology. We and others have suggested that genetic variants in 9p21.3 influence INK4/ARF gene expression; however, the mechanisms by which these distant polymorphisms (>100,000 bp away) influence transcription of the locus is unknown. The ASVD–associated genetic variants lie within the predicted structure of a non-coding RNA (ncRNA) called ANRIL. Based upon recent work suggesting that other ncRNAs can repress nearby coding genes, we considered the possibility that ANRIL structure may regulate INK4/ARF gene expression. Coupling molecular analysis with state-of-the-art sequencing technologies in a wide variety of cell types from normal human donors and cancer cells, we found that ANRIL encodes a heterogeneous species of rare RNA transcripts. Moreover, we identified novel, circular ANRIL isoforms (cANRIL) whose expression correlated with INK4/ARF transcription and ASVD risk. These studies suggest a new model wherein ANRIL structure influences INK4/ARF expression and susceptibility to atherosclerosis.
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Affiliation(s)
- Christin E. Burd
- The Curriculum in Toxicology, The Lineberger Comprehensive Cancer Center, The University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - William R. Jeck
- Department of Genetics, The University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Yan Liu
- Department of Genetics, The University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Hanna K. Sanoff
- The Division of Hematology and Oncology, University of Virginia, Charlottesville, Virginia, United States of America
| | - Zefeng Wang
- Department of Pharmacology, The University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Norman E. Sharpless
- The Curriculum in Toxicology, The Lineberger Comprehensive Cancer Center, The University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
- Department of Genetics, The University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
- Department of Medicine, The University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
- * E-mail:
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271
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Abstract
PURPOSE OF REVIEW The purpose of review is to describe the recent advances in the field of human epigenetics. RECENT FINDINGS With the completion of the genome project in 2003, high expectations existed for the DNA sequence information to provide answers about the causative mutations for common diseases. However, this was not completely the case. Another interesting finding that resulted from the genome project was that the perceived level of complexity of humans was not accompanied with a relative increase in the number of genes when compared to 'lower species'. Epigenetics is able to provide answers to previously unanswered health-related questions and can explain differences in level of complexity between organisms. Epigenetic studies accomplished in the last few years have exposed a very complex multilayered regulatory mechanism that is able to answer previously puzzling questions in biology. SUMMARY Understanding and interpretation of the role for epigenetic modifications in the human genome has progressed rapidly over the past decade with the advancement of microarray-based and sequence-based technologies. The complex interaction between DNA methylation, histone modifications, protein complexes and microRNAs has become better appreciated in the context of both local and long range epigenetic control of transcription in both normal cellular differentiation and tumorigenesis.
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Affiliation(s)
- Rocío M Rivera
- Division of Animal Sciences, University of Missouri, Columbia, Missouri, USA.
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272
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Cruickshanks HA, Adams PD. Chromatin: a molecular interface between cancer and aging. Curr Opin Genet Dev 2010; 21:100-6. [PMID: 21087854 DOI: 10.1016/j.gde.2010.10.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2010] [Revised: 10/11/2010] [Accepted: 10/19/2010] [Indexed: 01/04/2023]
Abstract
To prevent cancer, mammals have evolved potent tumor suppression mechanisms, including senescence and apoptosis. These processes depend on regulation of chromatin. Chromatin-dependent tumor suppressor pathways are activated in premalignant cells and tissues harboring cancer-causing genetic alterations, and also in normal aged tissue, the latter likely due to accumulation of genetic and cellular damage. Paradoxically, however, disruption of chromatin structure may also promote cancer. Apparent defects in chromatin structure accumulate with age, the biggest single risk factor for cancer. Evidence suggests that these age-associated perturbations in chromatin structure contribute to the age-associated increase in incidence of cancer. Thus, alterations in chromatin structure can both suppress and promote the onset of cancer, and both activities are inextricably linked to aging.
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Affiliation(s)
- Hazel A Cruickshanks
- University of Glasgow, CR-UK Beatson Labs, Garscube Estate, Switchback Road, Glasgow G61 1BD, United Kingdom
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273
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Salpeter SJ, Klein AM, Huangfu D, Grimsby J, Dor Y. Glucose and aging control the quiescence period that follows pancreatic beta cell replication. Development 2010; 137:3205-13. [PMID: 20823063 DOI: 10.1242/dev.054304] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Pancreatic beta cell proliferation has emerged as the principal mechanism for homeostatic maintenance of beta cell mass during adult life. This underscores the importance of understanding the mechanisms of beta cell replication and suggests novel approaches for regenerative therapy to treat diabetes. Here we use an in vivo pulse-chase labeling assay to investigate the replication dynamics of adult mouse beta cells. We find that replicated beta cells are able to re-enter the cell division cycle shortly after mitosis and regain their normal proliferative potential after a short quiescence period of several days. This quiescence period is lengthened with advanced age, but shortened during injury-driven beta cell regeneration and following treatment with a pharmacological activator of glucokinase, providing strong evidence that metabolic demand is a key determinant of cell cycle re-entry. Lastly, we show that cyclin D2, a crucial factor in beta cell replication, is downregulated during cell division, and is slowly upregulated post-mitosis by a glucose-sensitive mechanism. These results demonstrate that beta cells quickly regain their capacity to re-enter the cell cycle post-mitosis and implicate glucose control of cyclin D2 expression in the regulation of this process.
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Affiliation(s)
- Seth J Salpeter
- Department of Developmental Biology and Cancer Research and Molecular Biology, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
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274
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Butler AE, Cao-Minh L, Galasso R, Rizza RA, Corradin A, Cobelli C, Butler PC. Adaptive changes in pancreatic beta cell fractional area and beta cell turnover in human pregnancy. Diabetologia 2010; 53:2167-76. [PMID: 20523966 PMCID: PMC2931643 DOI: 10.1007/s00125-010-1809-6] [Citation(s) in RCA: 308] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/05/2010] [Accepted: 05/06/2010] [Indexed: 12/11/2022]
Abstract
AIMS/HYPOTHESIS We sought to establish the extent and basis for adaptive changes in beta cell numbers in human pregnancy. METHODS Pancreas was obtained at autopsy from women who had died while pregnant (n = 18), post-partum (n = 6) or were not pregnant at or shortly before death (controls; n = 20). Pancreases were evaluated for fractional pancreatic beta cell area, islet size and islet fraction of beta cells, beta cell replication (Ki67) and apoptosis (TUNEL), and indirect markers of beta cell neogenesis (insulin-positive cells in ducts and scattered beta cells in pancreas). RESULTS The pancreatic fractional beta cell area was increased by approximately 1.4-fold in human pregnancy, with no change in mean beta cell size. In pregnancy there were more small islets rather than an increase in islet size or beta cells per islet. No increase in beta cell replication or change in beta cell apoptosis was detected, but duct cells positive for insulin and scattered beta cells were increased with pregnancy. CONCLUSIONS/INTERPRETATION The adaptive increase in beta cell numbers in human pregnancy is not as great as in most reports in rodents. This increase in humans is achieved by increased numbers of beta cells in apparently new small islets, rather than duplication of beta cells in existing islets, which is characteristic of pregnancy in rodents.
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Affiliation(s)
- A. E. Butler
- Larry L. Hillblom Islet Research Center, UCLA David Geffen School of Medicine, 900 Veteran Ave, 24-130 Warren Hall, Los Angeles, CA 90095-7073 USA
| | - L. Cao-Minh
- Larry L. Hillblom Islet Research Center, UCLA David Geffen School of Medicine, 900 Veteran Ave, 24-130 Warren Hall, Los Angeles, CA 90095-7073 USA
| | - R. Galasso
- Larry L. Hillblom Islet Research Center, UCLA David Geffen School of Medicine, 900 Veteran Ave, 24-130 Warren Hall, Los Angeles, CA 90095-7073 USA
| | - R. A. Rizza
- Endocrine Research Unit, Department of Medicine, Mayo Clinic and Medical School, Rochester, MN USA
| | - A. Corradin
- Department of Information Engineering, University of Padua, Padua, Italy
| | - C. Cobelli
- Department of Information Engineering, University of Padua, Padua, Italy
| | - P. C. Butler
- Larry L. Hillblom Islet Research Center, UCLA David Geffen School of Medicine, 900 Veteran Ave, 24-130 Warren Hall, Los Angeles, CA 90095-7073 USA
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275
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Claiborn KC, Sachdeva MM, Cannon CE, Groff DN, Singer JD, Stoffers DA. Pcif1 modulates Pdx1 protein stability and pancreatic β cell function and survival in mice. J Clin Invest 2010; 120:3713-21. [PMID: 20811152 DOI: 10.1172/jci40440] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2009] [Accepted: 07/16/2010] [Indexed: 01/08/2023] Open
Abstract
The homeodomain transcription factor pancreatic duodenal homeobox 1 (Pdx1) is a major mediator of insulin transcription and a key regulator of the β cell phenotype. Heterozygous mutations in PDX1 are associated with the development of diabetes in humans. Understanding how Pdx1 expression levels are controlled is therefore of intense interest in the study and treatment of diabetes. Pdx1 C terminus-interacting factor-1 (Pcif1, also known as SPOP) is a nuclear protein that inhibits Pdx1 transactivation. Here, we show that Pcif1 targets Pdx1 for ubiquitination and proteasomal degradation. Silencing of Pcif1 increased Pdx1 protein levels in cultured mouse β cells, and Pcif1 heterozygosity normalized Pdx1 protein levels in Pdx1(+/-) mouse islets, thereby increasing expression of key Pdx1 transcriptional targets. Remarkably, Pcif1 heterozygosity improved glucose homeostasis and β cell function and normalized β cell mass in Pdx1(+/-) mice by modulating β cell survival. These findings indicate that in adult mouse β cells, Pcif1 limits Pdx1 protein accumulation and thus the expression of insulin and other gene targets important in the maintenance of β cell mass and function. They also provide evidence that targeting the turnover of a pancreatic transcription factor in vivo can improve glucose homeostasis.
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Affiliation(s)
- Kathryn C Claiborn
- Department of Medicine, Division of Endocrinology, Diabetes, and Metabolism and Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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276
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Ezh2, the histone methyltransferase of PRC2, regulates the balance between self-renewal and differentiation in the cerebral cortex. Proc Natl Acad Sci U S A 2010; 107:15957-62. [PMID: 20798045 DOI: 10.1073/pnas.1002530107] [Citation(s) in RCA: 325] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Multipotent progenitor cells of the cerebral cortex balance self-renewal and differentiation to produce complex neural lineages in a fixed temporal order in a cell-autonomous manner. We studied the role of the polycomb epigenetic system, a chromatin-based repressive mechanism, in controlling cortical progenitor cell self-renewal and differentiation. We found that the histone methyltransferase of polycomb repressive complex 2 (PCR2), enhancer of Zeste homolog 2 (Ezh2), is essential for controlling the rate at which development progresses within cortical progenitor cell lineages. Loss of function of Ezh2 removes the repressive mark of trimethylated histone H3 at lysine 27 (H3K27me3) in cortical progenitor cells and also prevents its establishment in postmitotic neurons. Removal of this repressive chromatin modification results in marked up-regulation in gene expression, the consequence of which is a shift in the balance between self-renewal and differentiation toward differentiation, both directly to neurons and indirectly via basal progenitor cell genesis. Although the temporal order of neurogenesis and gliogenesis are broadly conserved under these conditions, the timing of neurogenesis, the relative numbers of different cell types, and the switch to gliogenesis are all altered, narrowing the neurogenic period for progenitor cells and reducing their neuronal output. As a consequence, the timing of cortical development is altered significantly after loss of PRC2 function.
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277
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Collombat P, Xu X, Heimberg H, Mansouri A. Pancreatic beta-cells: from generation to regeneration. Semin Cell Dev Biol 2010; 21:838-44. [PMID: 20688184 DOI: 10.1016/j.semcdb.2010.07.007] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2010] [Accepted: 07/25/2010] [Indexed: 12/28/2022]
Abstract
The pancreas is composed of two main compartments consisting of endocrine and exocrine tissues. The majority of the organ is exocrine and responsible for the synthesis of digestive enzymes and for their transport via an intricate ductal system into the duodenum. The endocrine tissue represents less than 2% of the organ and is organized into functional units called islets of Langerhans, comprising alpha-, beta-, delta-, epsilon- and PP-cells, producing the hormones glucagon, insulin, somatostatin, ghrelin and pancreatic polypeptide (PP), respectively. Insulin-producing beta-cells play a central role in the control of the glucose homeostasis. Accordingly, absolute or relative deficiency in beta-cells may ultimately lead to type 1 and/or type 2 diabetes, respectively. One major goal of diabetes research is therefore to understand the molecular mechanisms controlling the development of beta-cells during pancreas morphogenesis, but also those underlying the regeneration of adult injured pancreas, and assess their significance for future cell-based therapy. In this review, we will therefore present new insights into beta-cell development with focus on beta-cell regeneration.
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278
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Abstract
In many tissues, mammalian aging is associated with a decline in the replicative and functional capacity of somatic stem cells and other self-renewing compartments. Understanding the basis of this decline is a major goal of aging research. In particular, therapeutic approaches to ameliorate or reverse the age-associated loss of stem function could be of use in clinical geriatrics. Such approaches include attempts to protect stem cells from age-promoting damage, to 'rejuvenate' stem cells through the use of pharmacologic agents that mitigate aging-induced alterations in signaling, and to replace lost stem cells through regenerative medicine approaches. Some headway has been made in each of these arenas over the last 18 months including advances in the production of donor-specific totipotent stem cells through induced pluripotency (iPS), gains in our understanding of how tumor suppressor signaling is controlled in self-renewing compartments to regulate aging, and further demonstration of extracellular 'milieu' factors that perturb stem cell function with age. This period has also been marked by the recent award of the Nobel Prize in Physiology or Medicine for elucidation of telomeres and telomerase, a topic of critical importance to stem cell aging.
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Affiliation(s)
- Norman E Sharpless
- Department of Medicine and Genetics, The University of North Carolina School of Medicine, Chapel Hill, NC 27599-7295, USA. nes@-med.unc.edu
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279
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Fiaschi-Taesch NM, Salim F, Kleinberger J, Troxell R, Cozar-Castellano I, Selk K, Cherok E, Takane KK, Scott DK, Stewart AF. Induction of human beta-cell proliferation and engraftment using a single G1/S regulatory molecule, cdk6. Diabetes 2010; 59:1926-36. [PMID: 20668294 PMCID: PMC2911074 DOI: 10.2337/db09-1776] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
OBJECTIVE Most knowledge on human beta-cell cycle control derives from immunoblots of whole human islets, mixtures of beta-cells and non-beta-cells. We explored the presence, subcellular localization, and function of five early G1/S phase molecules-cyclins D1-3 and cdk 4 and 6-in the adult human beta-cell. RESEARCH DESIGN AND METHODS Immunocytochemistry for the five molecules and their relative abilities to drive human beta-cell replication were examined. Human beta-cell replication, cell death, and islet function in vivo were studied in the diabetic NOD-SCID mouse. RESULTS Human beta-cells contain easily detectable cdks 4 and 6 and cyclin D3 but variable cyclin D1. Cyclin D2 was only marginally detectable. All five were principally cytoplasmic, not nuclear. Overexpression of the five, alone or in combination, led to variable increases in human beta-cell replication, with the cdk6/cyclin D3 combination being the most robust (15% versus 0.3% in control beta-cells). A single molecule, cdk6, proved to be capable of driving human beta-cell replication in vitro and enhancing human islet engraftment/proliferation in vivo, superior to normal islets and as effectively as the combination of cdk6 plus a D-cyclin. CONCLUSIONS Human beta-cells contain abundant cdk4, cdk6, and cyclin D3, but variable amounts of cyclin D1. In contrast to rodent beta-cells, they contain little or no detectable cyclin D2. They are primarily cytoplasmic and likely ineffective in basal beta-cell replication. Unexpectedly, cyclin D3 and cdk6 overexpression drives human beta-cell replication most effectively. Most importantly, a single molecule, cdk6, supports robust human beta-cell proliferation and function in vivo.
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Affiliation(s)
- Nathalie M Fiaschi-Taesch
- Division of Endocrinology, the University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
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280
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Rao RC, Tchedre KT, Malik MTA, Coleman N, Fang Y, Marquez VE, Chen DF. Dynamic patterns of histone lysine methylation in the developing retina. Invest Ophthalmol Vis Sci 2010; 51:6784-92. [PMID: 20671280 DOI: 10.1167/iovs.09-4730] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Histone lysine methylation (HKM) is an important epigenetic mechanism that establishes cell-specific gene expression and functions in development. However, epigenetic control of retinal development is poorly understood. To study the roles of HKM in retinogenesis, the authors examined the dynamic changes of three HKM modifications and of two of their regulators, the histone methyltransferases (HMTases) Ezh2 and G9a, in the mouse retina. METHODS Retinal sections and lysates from embryonic day 16 through adult were processed for immunohistochemistry and immunoblotting using antibodies against various marks and HMTases. To further analyze the biological functions of HKM, the effects of small molecule inhibitors of HMTases were examined in vitro. RESULTS Methylation marks of trimethyl lysine 4 and 27 on histone H3 (H3K4me3 and H3K27me3) were detected primarily in differentiated retinal neurons in the embryonic and adult retina. In contrast, dimethyl lysine 9 on histone H3 (H3K9me2) was noted in early differentiating retinal ganglion cells but was lost after birth. The HMTases controlling H3K27me3, H3K9me2, Ezh2, and G9a were enriched in the inner embryonic retina during the period of active retinogenesis. Using the chemical inhibitors of Ezh2 and G9a, the authors reveal a role for HKM in regulating retinal neuron survival. CONCLUSIONS HKM is a dynamic and spatiotemporally regulated process in the developing retina. Epigenetic regulation of gene transcription by Ezh2- and G9a-mediated HKM plays crucial roles in retinal neuron survival and may represent novel epigenetic targets to enhance viability in retinal neurodegenerative diseases such as glaucoma.
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Affiliation(s)
- Rajesh C Rao
- Schepens Eye Research Institute, Harvard Medical School, Boston, MA 02114, USA
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281
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Fu Z, Zhang W, Zhen W, Lum H, Nadler J, Bassaganya-Riera J, Jia Z, Wang Y, Misra H, Liu D. Genistein induces pancreatic beta-cell proliferation through activation of multiple signaling pathways and prevents insulin-deficient diabetes in mice. Endocrinology 2010; 151:3026-37. [PMID: 20484465 PMCID: PMC2903942 DOI: 10.1210/en.2009-1294] [Citation(s) in RCA: 147] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Genistein, a flavonoid in legumes and some herbal medicines, has various biological actions. However, studies on whether genistein has an effect on pancreatic beta-cell function are very limited. In the present study, we investigated the effect of genistein on beta-cell proliferation and cellular signaling related to this effect and further determined its antidiabetic potential in insulin-deficient diabetic mice. Genistein induced both INS1 and human islet beta-cell proliferation after 24 h of incubation, with 5 mum genistein inducing a maximal 27% increase. The effect of genistein on beta-cell proliferation was neither dependent on estrogen receptors nor shared by 17beta-estradiol or a host of structurally related flavonoid compounds. Pharmacological or molecular intervention of protein kinase A (PKA) or ERK1/2 completely abolished genistein-stimulated beta-cell proliferation, suggesting that both molecules are essential for genistein action. Consistent with its effect on cell proliferation, genistein induced cAMP/PKA signaling and subsequent phosphorylation of ERK1/2 in both INS1 cells and human islets. Furthermore, genistein induced protein expression of cyclin D1, a major cell-cycle regulator essential for beta-cell growth. Dietary intake of genistein significantly improved hyperglycemia, glucose tolerance, and blood insulin levels in streptozotocin-induced diabetic mice, concomitant with improved islet beta-cell proliferation, survival, and mass. These results demonstrate that genistein may be a natural antidiabetic agent by directly modulating pancreatic beta-cell function via activation of the cAMP/PKA-dependent ERK1/2 signaling pathway.
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Affiliation(s)
- Zhuo Fu
- Department of Human Nutrition, Foods, and Exercise, Virginia Polytechnic Institute and State University, Blacksburg, VA 24060, USA
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282
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The polycomb group gene product Ezh2 regulates proliferation and differentiation of murine hepatic stem/progenitor cells. J Hepatol 2010; 52:854-63. [PMID: 20395008 DOI: 10.1016/j.jhep.2010.01.027] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/18/2009] [Revised: 01/12/2010] [Accepted: 01/14/2010] [Indexed: 01/21/2023]
Abstract
BACKGROUND & AIMS Polycomb group proteins initiate and maintain gene silencing through chromatin modifications and contribute to the maintenance of self-renewal in a variety of stem cells. Among polycomb repressive complexes (PRCs), PRC2 initiates gene silencing by methylating histone H3 lysine 27, and PRC1 maintains gene silencing through mono-ubiquitination of histone H2A lysine 119. We have previously shown that Bmi1, a core component of PRC1, tightly regulates the self-renewal of hepatic stem/progenitor cells. METHODS In this study, we conducted lentivirus-mediated knockdown of Ezh2 to characterise the function of Ezh2, a major component of PRC2, in hepatic stem/progenitor cells. RESULTS Loss of Ezh2 function in embryonic murine hepatic stem/progenitor cells severely impaired proliferation and self-renewal capability. This effect was more prominent than that of Bmi1-knockdown and was partially abrogated by the deletion of both Ink4a and Arf, major targets of PRC1 and PRC2. Importantly, Ezh2-knockdown but not Bmi1-knockdown promoted the differentiation and terminal maturation of hepatocytes, followed by the up-regulation of several transcriptional regulators of hepatocyte differentiation. CONCLUSIONS Our findings indicate that Ezh2 plays an essential role in the maintenance of both the proliferative and self-renewal capacity of hepatic stem/progenitor cells and the full execution of their differentiation.
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283
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Tissue-specific p19Arf regulation dictates the response to oncogenic K-ras. Proc Natl Acad Sci U S A 2010; 107:10184-9. [PMID: 20479239 DOI: 10.1073/pnas.1004796107] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The ability of oncogenes to engage tumor suppressor pathways represents a key regulatory mechanism that can limit the outgrowth of incipient tumor cells. For example, in a number of settings oncogenic Ras strongly activates the Ink4a/Arf locus, resulting in cell cycle arrest or senescence. The capacity of different cell types to execute tumor suppressor programs following expression of endogenous K-ras(G12D) in vivo has not been examined. Using compound mutant mice containing the Arf(GFP) reporter and the spontaneously activating K-ras(LA2) allele, we have uncovered dramatic tissue specificity of K-ras(G12D)-dependent p19(Arf) up-regulation. Lung tumors, which can arise in the presence of functional p19(Arf), rarely display p19(Arf) induction. In contrast, sarcomas always show robust activation, which correlates with genetic evidence, suggesting that loss of the p19(Arf)-p53 pathway is a requisite event for sarcomagenesis. Using constitutive and inducible RNAi systems in vivo, we highlight cell type-specific chromatin regulation of Ink4a/Arf as a critical determinant of cellular responses to oncogenic K-ras. Polycomb-group complexes repress the locus in lung tumors, whereas the SWI/SNF family member Snf5 acts as an important mediator of p19(Arf) induction in sarcomas. This variation in tumor suppressor induction might explain the inherent differences between tissues in their sensitivity to Ras-mediated transformation.
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284
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Villeneuve LM, Natarajan R. The role of epigenetics in the pathology of diabetic complications. Am J Physiol Renal Physiol 2010; 299:F14-25. [PMID: 20462972 DOI: 10.1152/ajprenal.00200.2010] [Citation(s) in RCA: 227] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Diabetes is associated with significantly accelerated rates of several debilitating microvascular complications such as nephropathy, retinopathy, and neuropathy, and macrovascular complications such as atherosclerosis and stroke. While several studies have been devoted to the evaluation of genetic factors related to type 1 and type 2 diabetes and associated complications, much less is known about epigenetic changes that occur without alterations in the DNA sequence. Environmental factors and nutrition have been implicated in diabetes and can also affect epigenetic states. Exciting research has shown that epigenetic changes in chromatin can affect gene transcription in response to environmental stimuli, and changes in key chromatin histone methylation patterns have been noted under diabetic conditions. Reports also suggest that epigenetics may be involved in the phenomenon of metabolic memory observed in clinic trials and animal studies. Further exploration into epigenetic mechanisms can yield new insights into the pathogenesis of diabetes and its complications and uncover potential therapeutic targets and treatment options to prevent the continued development of diabetic complications even after glucose control has been achieved.
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Affiliation(s)
- Louisa M Villeneuve
- Department of Diabetes, Beckman Research Institute of City of Hope, Duarte, California 91010, USA
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285
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van Arensbergen J, García-Hurtado J, Moran I, Maestro MA, Xu X, Van de Casteele M, Skoudy AL, Palassini M, Heimberg H, Ferrer J. Derepression of Polycomb targets during pancreatic organogenesis allows insulin-producing beta-cells to adopt a neural gene activity program. Genome Res 2010; 20:722-32. [PMID: 20395405 DOI: 10.1101/gr.101709.109] [Citation(s) in RCA: 129] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The epigenome changes that underlie cellular differentiation in developing organisms are poorly understood. To gain insights into how pancreatic beta-cells are programmed, we profiled key histone methylations and transcripts in embryonic stem cells, multipotent progenitors of the nascent embryonic pancreas, purified beta-cells, and 10 differentiated tissues. We report that despite their endodermal origin, beta-cells show a transcriptional and active chromatin signature that is most similar to ectoderm-derived neural tissues. In contrast, the beta-cell signature of trimethylated H3K27, a mark of Polycomb-mediated repression, clusters with pancreatic progenitors, acinar cells and liver, consistent with the epigenetic transmission of this mark from endoderm progenitors to their differentiated cellular progeny. We also identified two H3K27 methylation events that arise in the beta-cell lineage after the pancreatic progenitor stage. One is a wave of cell-selective de novo H3K27 trimethylation in non-CpG island genes. Another is the loss of bivalent and H3K27me3-repressed chromatin in a core program of neural developmental regulators that enables a convergence of the gene activity state of beta-cells with that of neural cells. These findings reveal a dynamic regulation of Polycomb repression programs that shape the identity of differentiated beta-cells.
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Affiliation(s)
- Joris van Arensbergen
- Genomic Programming of Beta Cells Laboratory, Institut d'Investigacions Biomèdiques August Pi i Sunyer, Barcelona 08036, Spain
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286
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Abstract
The pancreas has been the subject of intense research due to the debilitating diseases that result from its dysfunction. In this review, we summarize current understanding of the critical tissue interactions and intracellular regulatory events that take place during formation of the pancreas from a small cluster of cells in the foregut domain of the mouse embryo. Importantly, an understanding of principles that govern the development of this organ has equipped us with the means to manipulate both embryonic and differentiated adult cells in the context of regenerative medicine. The emerging area of lineage modulation within the adult pancreas is of particular interest, and this review summarizes recent findings that exemplify how lessons learned from development are being applied to reveal the potential of fully differentiated cells to change fate.
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Affiliation(s)
- Sapna Puri
- Diabetes Center, Department of Medicine, University of California, San Francisco, CA 94143, USA
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287
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McKnight KD, Wang P, Kim SK. Deconstructing pancreas development to reconstruct human islets from pluripotent stem cells. Cell Stem Cell 2010; 6:300-308. [PMID: 20362535 PMCID: PMC3148083 DOI: 10.1016/j.stem.2010.03.003] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
There is considerable excitement about harnessing the potential of human stem cells to replace pancreatic islets that are destroyed in type 1 diabetes mellitus. However, our current understanding of the mechanisms underlying pancreas and islet ontogeny has come largely from the powerful genetic, developmental, and embryological approaches available in nonhuman organisms. Successful islet reconstruction from human pluripotent cells will require greater attention to "deconstructing" human pancreas and islet developmental biology and consistent application of conditional genetics, lineage tracing, and cell purification to stem cell biology.
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Affiliation(s)
- Kristen D McKnight
- Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305-5329, USA
| | - Pei Wang
- Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305-5329, USA
| | - Seung K Kim
- Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305-5329, USA; Department of Medicine (Oncology Division), Stanford University School of Medicine, Stanford, CA 94305-5329, USA; Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305-5329, USA.
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288
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Blagosklonny MV, Campisi J, Sinclair DA, Bartke A, Blasco MA, Bonner WM, Bohr VA, Brosh RM, Brunet A, Depinho RA, Donehower LA, Finch CE, Finkel T, Gorospe M, Gudkov AV, Hall MN, Hekimi S, Helfand SL, Karlseder J, Kenyon C, Kroemer G, Longo V, Nussenzweig A, Osiewacz HD, Peeper DS, Rando TA, Rudolph KL, Sassone-Corsi P, Serrano M, Sharpless NE, Skulachev VP, Tilly JL, Tower J, Verdin E, Vijg J. Impact papers on aging in 2009. Aging (Albany NY) 2010; 2:111-21. [PMID: 20351400 PMCID: PMC2871240 DOI: 10.18632/aging.100132] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2010] [Accepted: 03/22/2010] [Indexed: 01/09/2023]
Abstract
The editorial board of Aging reviews research papers published in 2009, which they
believe have or will have a significant impact on aging research. Among many
others, the topics include genes that accelerate aging or in contrast promote
longevity in model organisms, DNA damage responses and telomeres, molecular
mechanisms of life span extension by calorie restriction and pharmacologic
interventions into aging. The emerging message in 2009 is that aging is not
random but determined by a genetically-regulated longevity network and can be
decelerated both genetically and pharmacologically.
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289
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Rieck S, Kaestner KH. Expansion of beta-cell mass in response to pregnancy. Trends Endocrinol Metab 2010; 21:151-8. [PMID: 20015659 PMCID: PMC3627215 DOI: 10.1016/j.tem.2009.11.001] [Citation(s) in RCA: 251] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2009] [Revised: 11/06/2009] [Accepted: 11/09/2009] [Indexed: 12/22/2022]
Abstract
Inadequate beta-cell mass can lead to insulin insufficiency and diabetes. During times of prolonged metabolic demand for insulin, the endocrine pancreas can respond by increasing beta-cell mass, both by increasing cell size and by changing the balance between beta-cell proliferation and apoptosis. In this paper, we review recent advances in our understanding of the mechanisms that control the adaptive expansion of beta-cell mass, focusing on the islet's response to pregnancy, a physiological state of insulin resistance. Functional characterization of factors controlling both beta-cell proliferation and survival might not only lead to the development of successful therapeutic strategies to enhance the response of the beta-cell to increased metabolic loads, but also improve islet transplantation regimens.
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Affiliation(s)
- Sebastian Rieck
- Department of Genetics and Institute for Diabetes, Obesity and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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290
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Leeb M, Pasini D, Novatchkova M, Jaritz M, Helin K, Wutz A. Polycomb complexes act redundantly to repress genomic repeats and genes. Genes Dev 2010; 24:265-76. [PMID: 20123906 DOI: 10.1101/gad.544410] [Citation(s) in RCA: 264] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Polycomb complexes establish chromatin modifications for maintaining gene repression and are essential for embryonic development in mice. Here we use pluripotent embryonic stem (ES) cells to demonstrate an unexpected redundancy between Polycomb-repressive complex 1 (PRC1) and PRC2 during the formation of differentiated cells. ES cells lacking the function of either PRC1 or PRC2 can differentiate into cells of the three germ layers, whereas simultaneous loss of PRC1 and PRC2 abrogates differentiation. On the molecular level, the differentiation defect is caused by the derepression of a set of genes that is redundantly repressed by PRC1 and PRC2 in ES cells. Furthermore, we find that genomic repeats are Polycomb targets and show that, in the absence of Polycomb complexes, endogenous murine leukemia virus elements can mobilize. This indicates a contribution of the Polycomb group system to the defense against parasitic DNA, and a potential role of genomic repeats in Polycomb-mediated gene regulation.
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Affiliation(s)
- Martin Leeb
- Research Institute of Molecular Pathology, Dr. Bohr-Gasse 7, 1030 Vienna, Austria
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291
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Abstract
Type 1 and Type 2 diabetes are complex diseases associated with multiple complications, and both genetic and environmental factors have been implicated in these pathologies. While numerous studies have provided a wealth of knowledge regarding the genetics of diabetes, the mechanistic pathways leading to diabetes and its complications remain only partly understood. Studying the role of epigenetics in diabetic complications can provide valuable new insights to clarify the interplay between genes and the environment. DNA methylation and histone modifications in nuclear chromatin can generate epigenetic information as another layer of gene transcriptional regulation sensitive to environmental signals. Recent evidence shows that key biochemical pathways and epigenetic chromatin histone methylation patterns are altered in target cells under diabetic conditions and might also be involved in the metabolic memory phenomenon noted in clinical trials and animal studies. New therapeutic targets and treatment options could be uncovered from an in-depth study of the epigenetic mechanisms that might perpetuate diabetic complications despite glycemic control.
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Affiliation(s)
- Louisa M Villeneuve
- Division of Diabetes, Beckman Research Institute of City of Hope, 1500 E. Duarte Road, Duarte, CA-91010, USA
| | - Rama Natarajan
- Author for correspondence: Division of Diabetes, Beckman Research Institute of City of Hope, 1500 East Duarte Road, Duarte, CA-91010, USA, Tel.: +1 626 256 4673 ext. 62289, Fax: +1 626 301 8136,
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292
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Adams PD. Healing and hurting: molecular mechanisms, functions, and pathologies of cellular senescence. Mol Cell 2009; 36:2-14. [PMID: 19818705 DOI: 10.1016/j.molcel.2009.09.021] [Citation(s) in RCA: 242] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2009] [Indexed: 01/07/2023]
Abstract
Cellular senescence is a proliferation arrest that is typically irreversible and caused by various cellular stresses, including excess rounds of cell division and cancer-causing genetic alterations. Senescence actively contributes to a tissue-level response to tissue wounding and incipient cancer, healing the tissue and suppressing tumor formation. However, in the long term, the same senescence program may hurt the tissue, thereby contributing to tissue aging. Tumor suppression, wound healing, and aging are each associated with inflammation, and here it is proposed that cellular senescence contributes to a "nonimmune cell" component of the tissue inflammatory response.
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Affiliation(s)
- Peter D Adams
- Cancer Research UK Beatson Labs, University of Glasgow, Glasgow G61 1BD, UK.
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293
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Kheradmand Kia S, Solaimani Kartalaei P, Farahbakhshian E, Pourfarzad F, von Lindern M, Verrijzer CP. EZH2-dependent chromatin looping controls INK4a and INK4b, but not ARF, during human progenitor cell differentiation and cellular senescence. Epigenetics Chromatin 2009; 2:16. [PMID: 19954516 PMCID: PMC3225837 DOI: 10.1186/1756-8935-2-16] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2009] [Accepted: 12/02/2009] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The INK4b-ARF-INK4a tumour suppressor locus controls the balance between progenitor cell renewal and cancer. In this study, we investigated how higher-order chromatin structure modulates differential expression of the human INK4b-ARF-INK4a locus during progenitor cell differentiation, cellular ageing and senescence of cancer cells. RESULTS We found that INK4b and INK4a, but not ARF, are upregulated following the differentiation of haematopoietic progenitor cells, in ageing fibroblasts and in senescing malignant rhabdoid tumour cells. To investigate the underlying molecular mechanism we analysed binding of polycomb group (PcG) repressive complexes (PRCs) and the spatial organization of the INK4b-ARF-INK4a locus. In agreement with differential derepression, PcG protein binding across the locus is discontinuous. As we described earlier, PcG repressors bind the INK4a promoter, but not ARF. Here, we identified a second peak of PcG binding that is located approximately 3 kb upstream of the INK4b promoter. During progenitor cell differentiation and ageing, PcG silencer EZH2 attenuates, causing loss of PRC binding and transcriptional activation of INK4b and INK4a. The expression pattern of the locus is reflected by its organization in space. In the repressed state, the PRC-binding regions are in close proximity, while the intervening chromatin harbouring ARF loops out. Down regulation of EZH2 causes release of the approximately 35 kb repressive chromatin loop and induction of both INK4a and INK4b, whereas ARF expression remains unaltered. CONCLUSION PcG silencers bind and coordinately regulate INK4b and INK4a, but not ARF, during a variety of physiological processes. Developmentally regulated EZH2 levels are one of the factors that can determine the higher order chromatin structure and expression pattern of the INK4b-ARF-INK4a locus, coupling human progenitor cell differentiation to proliferation control. Our results revealed a chromatin looping mechanism of long-range control and argue against models involving homogeneous spreading of PcG silencers across the INK4b-ARF-INK4a locus.
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Affiliation(s)
- Sima Kheradmand Kia
- Department of Biochemistry, Center for Biomedical Genetics, Erasmus University Medical Center, PO Box 1738, 3000 DR Rotterdam, The Netherlands.
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294
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Affiliation(s)
- Charlotte Ling
- Department of Clinical Sciences, Lund University Diabetes Center, Lund University, Malmö, Sweden.
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295
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Abstract
The Polycomb group (PcG) proteins are transcriptional repressors that regulate lineage choices during development and differentiation. Recent studies have advanced our understanding of how the PcG proteins regulate cell fate decisions and how their deregulation potentially contributes to cancer. In this Review we discuss the emerging roles of long non-coding RNAs (ncRNAs) and a subset of transcription factors, which we call cell fate transcription factors, in the regulation of PcG association with target genes. We also speculate about how their deregulation contributes to tumorigenesis.
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Affiliation(s)
- Adrian P Bracken
- The Smurfit Institute of Genetics, Trinity College Dublin and The Adelaide & Meath Hospital, including the National Children's Hospital, Dublin, Ireland.
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296
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Le Guezennec X, Bulavin DV. WIP1 phosphatase at the crossroads of cancer and aging. Trends Biochem Sci 2009; 35:109-14. [PMID: 19879149 DOI: 10.1016/j.tibs.2009.09.005] [Citation(s) in RCA: 110] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2009] [Revised: 09/10/2009] [Accepted: 09/10/2009] [Indexed: 01/07/2023]
Abstract
The PP2C family serine/threonine phosphatase WIP1 is characterized by distinctive oncogenic properties mediated by inhibitory functions on several tumor suppressor pathways, including ATM, CHK2, p38MAPK and p53. PPM1D, the gene encoding WIP1, is aberrantly amplified in different types of human primary cancers, and its deletion in mice results in a profound tumor-resistant phenotype. Numerous downstream targets of WIP1 have been identified, and genetic studies confirm that some play a part in tumorigenesis. Recent evidence highlights a new role for WIP1 in the regulation of a cell-autonomous decline in proliferation of certain self-renewing cell types, including pancreatic beta-cells, with advancing age. These emerging functions of WIP1 make it a potent therapeutic target against cancer and aging.
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Affiliation(s)
- Xavier Le Guezennec
- Institute of Molecular and Cell Biology, Cell Cycle Control and Tumorigenesis Group, 61 Biopolis Drive, Proteos, Singapore
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297
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A quantitative model for age-dependent expression of the p16INK4a tumor suppressor. Proc Natl Acad Sci U S A 2009; 106:16562-7. [PMID: 19805338 DOI: 10.1073/pnas.0904405106] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Recent work has shown that expression of the p16(INK4a) tumor suppressor increases with chronological age. Expression is accelerated by gerontogenic behaviors such as tobacco use and physical inactivity, and is also influenced by allelic genotype of a polymorphic single nucleotide polymorphism (SNP) rs10757278 that is physically linked with the p16(INK4a) ORF. To understand the relationship between p16(INK4a) expression, chronologic age, subject characteristics and host genetics, we sought to develop a mathematical model that links p16(INK4a) expression with aging. Using an annotated dataset of 170 healthy adults for whom p16(INK4a) expression and subject genotypes were known, we developed two alternative stochastic models that relate p16(INK4a) expression to age, smoking, exercise and rs10757278 genotype. Levels of p16(INK4a) increased exponentially and then saturated at later chronologic ages. The model, which best fit the data, suggests saturation occurs because of p16(INK4a)-dependent attrition of subjects at older chronologic ages, presumably due to death or chronic illness. An important feature of our model is that factors that contribute to death in a non p16(INK4a)-dependent manner do not affect our analysis. Interestingly, tobacco-related increases in p16(INK4a) expression are predicted to arise from a decrease in the rate of p16(INK4a)-dependent death. This analysis is most consistent with the model that p16(INK4a) expression monotonically increases with age, and higher expression is associated with increased subject attrition.
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298
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Liu Y, Sanoff HK, Cho H, Burd CE, Torrice C, Ibrahim JG, Thomas NE, Sharpless NE. Expression of p16(INK4a) in peripheral blood T-cells is a biomarker of human aging. Aging Cell 2009; 8:439-48. [PMID: 19485966 DOI: 10.1111/j.1474-9726.2009.00489.x] [Citation(s) in RCA: 326] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Expression of the p16(INK4a) tumor suppressor sharply increases with age in most mammalian tissues, and contributes to an age-induced functional decline of certain self-renewing compartments. These observations have suggested that p16(INK4a) expression could be a biomarker of mammalian aging. To translate this notion to human use, we determined p16(INK4a) expression in cellular fractions of human whole blood, and found highest expression in peripheral blood T-lymphocytes (PBTL). We then measured INK4/ARF transcript expression in PBTL from two independent cohorts of healthy humans (170 donors total), and analyzed their relationship with donor characteristics. Expression of p16(INK4a), but not other INK4/ARF transcripts, appeared to exponentially increase with donor chronologic age. Importantly, p16(INK4a) expression did not independently correlate with gender or body-mass index, but was significantly associated with tobacco use and physical inactivity. In addition, p16(INK4a) expression was associated with plasma interleukin-6 concentration, a marker of human frailty. These data suggest that p16(INK4a) expression in PBTL is an easily measured, peripheral blood biomarker of molecular age.
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Affiliation(s)
- Yan Liu
- Department of Genetics, The University of North Carolina School of Medicine, Chapel Hill, USA
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299
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Liu Y, Sharpless NE. Tumor suppressor mechanisms in immune aging. Curr Opin Immunol 2009; 21:431-9. [PMID: 19535234 DOI: 10.1016/j.coi.2009.05.011] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2009] [Revised: 05/07/2009] [Accepted: 05/08/2009] [Indexed: 12/22/2022]
Abstract
The cancer-aging hypothesis suggests that the activation of some tumor suppressor mechanisms beneficially prevents cancer but also untowardly promotes mammalian aging. Along these lines, activation of tumor suppressor mechanisms that inhibit the cell cycle (e.g. p16(INK4a) and p53) in response to DNA damage and other age-promoting stimuli has taken center stage in immune-aging research. Immune cells are intrinsically susceptible to transforming events due to V(D)J recombination, a high rate of cellular turnover and requisite long-term self-renewal. Therefore, the DNA damage response and cell cycle regulation play a clear role in maintaining homeostasis without neoplastic progression. Here we will argue on the basis of recent advances in our understanding of tumor suppressor mechanisms in immune cells; however, that aspects of these same beneficial pathways have the potential to induce intrinsic immune aging.
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Affiliation(s)
- Yan Liu
- Department of Genetics and Medicine, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA
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