TELOMERE BIOLOGY IN METAZOA NUNO M. V. TELOMERE BIOLOGY IN METAZOA Nuno M. V. Gomes, D.V.M.,

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  • UNIVERSIDADE DE LISBOA

    FACULDADE DE CINCIAS

    DEPARTAMENTO DE FSICA

    TELOMERE BIOLOGY IN METAZOA

    NUNO M. V. GOMES

    DOUTORAMENTO EM ENGENHARIA BIOMDICA E BIOFSICA

    2011

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    UNIVERSIDADE DE LISBOA

    FACULDADE DE CINCIAS

    DEPARTAMENTO DE FSICA

    TELOMERE BIOLOGY IN METAZOA

    NUNO M. V. GOMES

    Thesis supervised by:

    Prof. Doutor Jerry W. Shay The University of Texas Southwestern Medical Center at Dallas

    Prof. Doutor Eduardo Ducla-Soares Institute of Biophysics and Biomedical Engineering University of Lisbon

    DOUTORAMENTO EM ENGENHARIA BIOMDICA E BIOFSICA

    2011

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    DEDICATION

    Dedicated to my wonderful family

    for brightening every day of my life.

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    Copyright

    by

    Nuno M. V. Gomes, 2011

    All Rights Reserved

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    ACKNOWLEDGMENTS

    I am grateful to my mentors Jerry Shay and Woodring Wright, from the Department of

    Cell Biology of the University of Texas Southwestern Medical Center at Dallas, for the

    opportunity to train in their laboratory and their daily teachings and support. Their

    training provided solid foundations for the development of my scientific skills and critical

    thinking, turning my mental clock from deductive thinking into inductive reasoning.

    I would like to thank the Faculty of the Institute of Biophysics and Biomedical

    Engineering, in particular Professor Ducla-Soares for its advice and supervision. I would

    also like to thank my fellow colleagues of the IBEB with whom I had the privilege to

    study. It was an honor to study side by side with these bright and creative group of

    physicists, engineers and chemists.

    I would also like to thank the Shay/Wright lab members, past and present, for their

    teachings and kind help. In particular would like to acknowledge Michael Wang, Maeve

    Hsieh, William Walker and Donna Meng, for their great help advancing this project. I

    thank also Nicholas Forsyth, for his insightful discussions and Ying Zou for the excellent

    imaging training. Im thankful to the amazing Kevin Kennon, for making sure all

    administrative issues were properly and timely done, for his friendship and good spirit.

    Im grateful to Oliver A. Ryder, Marlys L. Houck, Suellen J. Charter

    and other from the

    Conservation and Research for Endangered Species, Genetics Division of the San Diego

    Zoo, for their contribution with the animal cells and useful information provided.

    I thank Steven N. Austad and his team from the Barshop Center for Longevity and

    Aging Studies in San Antonio, Texas for providing animal cells and for their insighfull

    discussions and ideas.

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    I also thank John Wise and the National Marine Sanctuary Foundation for providing the

    Bowhead Whale lung cells.

    I thank Chris Vendetti from the University of Reading and Mark Pagel from the

    University of Reading and Santa F Institute in New Mexico for their amazing help with

    the filogenetic statistical analyses.

    To the faculty and students happydauers of the Aging course of the Woods Hole

    Marine Biological Laboratory for opening my mind to the exciting research in the aging

    field and for their past and present aging research discussions and updates.

    This work was supported by the European Union Programs POCI 2010 & FSE and by

    national funds from the Portuguese Ministry for Science, Technology and Superior

    Education ((N.M.V.G) and by the Keck Foundation and the National Institute on Aging

    (W.E.W. & J.W.S.).

    I am deeply grateful to my family for always being there for me, brightening my life

    and supporting my crazy scientific endeavors.

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    TELOMERE BIOLOGY IN METAZOA

    Nuno M. V. Gomes, D.V.M., M.Sc.

    University of Lisbon, 2011

    Supervising Professors: Jerry W. Shay, Ph.D. and Eduardo Ducla-Soares, Ph.D.

    ABSTRACT

    Telomerase, the enzyme that maintains telomeres, is absent from most adult

    human somatic cells, producing a progressive telomere shortening that limits the

    proliferative potential of primary human cell cultures (Shay and Wright 2007). This

    programmed telomere shortening, replicative aging, functions as a tumor suppressor

    program that generates a barrier for the outgrowth of tumors. Remarkably, this telomere

    tumor suppressor program is not conserved in laboratory rats and mice, which have long

    telomeres and constitutive telomerase (Sherr and DePinho 2000; Wright and Shay 2000).

    The present study examines over 60 mammalian species to determine the phylogenetic

    distribution of the telomere tumor suppressor pathway. Phylogeny based statistical

    analysis demonstrates that telomere length inversely correlates with lifespan but not body

    size, while telomerase expression inversely correlates with body size but not lifespan.

    The ancestral mammalian phenotype was determined to have short telomeres and

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    repressed telomerase. At least 5-7 independent times in different orders smaller, shorter

    lived species changed to having long telomeres and expressing telomerase, suggesting

    tradeoffs between the advantages and drawbacks of using replicative aging as a tumor

    suppression mechanism. We show that one advantage is consistent with reducing the

    energetic/cellular costs of specific oxidative protection mechanism needed to maintain

    short telomeres. We propose that the telomere tumor suppressor pathway represents an

    initial adaptation to the increased mutational load of homeothermy by ancestral

    mammals, has adaptive advantage in large and long-lived animals, but has been

    abandoned by many species. These observations resolve a longstanding confusion about

    the use of telomeres in humans and mice, support a role for telomere length in limiting

    lifespan, provide a critical framework for interpreting studies of the role of oxidative

    protection in the biology of aging, and identify which mammals can be used as

    appropriate model organisms for the study of the role of telomeres in human cancer and

    aging.

    keywords: evolution. telomeres, telomerase, senescence, mammals

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    RESUMO

    As clulas somticas humanas normais exibem uma capacidade proliferativa

    limitada, um fenmeno conhecido como limite de Hayflick. As clulas fetais dividem-

    se mais vezes em cultura do que as de uma criana, que por sua vez se dividem mais do

    que as de um adulto. Os telmeros so os relgios moleculares que permitem s clulas

    contarem o seu nmero de divises. Os telmeros so as sequncias repetitivas de ADN

    encontradas nos extremos dos cromossomas lineares. Cada um dos 92 telmeros

    humanos contm milhares de repeties da sequncia de seis nucletidos TTAGGG e as

    protenas associadas aos telmeros. O comprimento dos telmeros diminui quer em

    funo da idade dos tecidos do dador, quer com o nmero de divises celulares em

    cultura.

    A telomerase uma ribonucleoproteina celular transcriptase reversa que utiliza o

    seu componente cataltico (hTERT) para sintetizar ADN telomrico (TTAGGG)n

    directamente nas extremidades dos cromossomas. Em humanos, esta enzima expressa

    em tecidos embrionrios e em clulas germinais especficas, mas no detectada na

    maioria das clulas somticas normais, o que conduz a um encurtamento progressivo dos

    telmeros que limita o potencial proliferativo das clulas primrias humanas.

    Este encurtamento programado dos telmeros - senescncia replicativa funciona

    como um programa supressor tumoral que gera uma barreira contra o sobrecrescimento

    tumoral (85% dos tumores humanos possuem actividade da enzima telomerase e so

    capazes de manter os seus telmeros). Notavelmente, este programa supressor tumoral

    telomrico no se encontra preservado nas ratazanas e nos ratos de laboratrio, que tm

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    telmeros longos e telomerase constitutiva. O estudo presente examina mais de 60

    espcies de mamferos de modo a determinar a distribuio filogentica deste mecanismo

    supressor tumoral.

    A expresso de telomerase em culturas de fibroblastos em diviso provenientes de

    dadores adultos foi usada para determinar a fora da represso da telomerase em clulas

    somticas mesenquimatosas. As clulas cultivadas em condies no ideais (ex: falta de

    um micronutriente, oxignio a 20%), exibem frequentemente uma paragem de diviso

    chamada estase (STASIS- stress or aberrante signaling induced senescence), que

    independente do encurtamento telomrico. A presena de estase cedo (dentro de 15

    duplicaes) tambm forneceu um fentipo adicional.

    Neste estudo examinei a expresso da telomerase, o comprimento dos telmeros,

    o peso corporal e a longevidade. Usando o resultado da anlise de modelos de regresso

    que levam em linha de conta a ascendncia comum, prevista pela filogenia dentro de uma

    matriz filogentica dos quadrados mnimos (PGLS) verifica-se que a expresso da

    telomerase se correlaciona de modo significativo com o inverso da massa corporal

    (p=0.0082), mas no apresenta efeitos independentes com a longevidade (p=0.34). A

    mesma anlise demonstrou que o comprimento dos telmeros apresenta uma significativa

    correlao negativa com a longevidade (p=0.0032) acima do previsto pela massa c