Manifestation of Novel Social Challenges of the European Unionin the Teaching Material ofMedical Biotechnology Master’s Programmesat the University of Pécs and at the University of DebrecenIdentification number: TÁMOP-4.1.2-08/1/A-2009-0011

AGING AND GENE EXPRESSION – ALTERATIONS OF THE GENOME DUE TO AGING

Krisztián KvellMolecular and Clinical Basics of Gerontology – Lecture 22

Manifestation of Novel Social Challenges of the European Unionin the Teaching Material ofMedical Biotechnology Master’s Programmesat the University of Pécs and at the University of DebrecenIdentification number: TÁMOP-4.1.2-08/1/A-2009-0011

TÁMOP-4.1.2-08/1/A-2009-0011

TT A G GT

GDNA

RNA template

Telomerase

Nucleotides

AA U C CC A

Telomere sequence andtelomerase function

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• Most favored clock, but cause or marker?

• Sequence: TTAGGG hexanucleotide > 1000x

• Polymerase leaves gap with every replication

• Oxidative stress accelerates telomere loss rate

Telomeres as biological clocks

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• Telomeres form terminal loops for stability

• Role of TRF2 in telomere stability• Issue of telomere length threshold• Issue of telomere loss rate vs. stress

rate

Factors influencing telomere loss rate

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Telomere is repetitive DNA sequence

Embyonic stem cells

Adultstem cells

Telomerelong

Telomereshort

Active telomerase

Telomerase inactive

or absent

AA T C CCTT A G GG

Changes in telomere length

Chromosome

Extending the length of a telomere

New DNAShort end of DNA

GG T T

AA U C CC A A U CRNA templateT CC C C A TAC C A A

T T A GA G G G

TelomeraseDNA polymerase

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• Counteracting (oxidative) stress conditions

• Telomerase activity increases telomere length

• ALT: alternative telomere lengthening

Slowing, reversing telomere shortening

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Telomerase reactivation

Further evolutionLoss of telomere function

Significance of telomere in cancer

Telomere lenght

Number of aberrations

Genome instability

Normal tissue Hyperplasia Carcinoma in situ

Telomerecrisis

Invasive cancer

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• Soluble factors / cell non-autonomous spreading

• Pineal clock, role of melatonin• Circadian clock mechanisms• DNA methylation, acetylation, de-

acetylation

Further clocks ticking

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• Werner-syndrome• Cockayne syndrome• Hutchinson-Guilford progeria• Xeroderma pigmentosum

Genomic instability in progeria types

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• Homozygous recessive (skin, cataract, diabetes mellitus osteoporosis)

• WRN protein (anti-recombinase, helicase, removes recombination and repair intermediates)

• Defective transcription (50%)• Relation with p53 (attenuated

apoptosis)• Increased telomere loss rate

Werner syndrome

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• Rare segmental progeria (dwarfism, photosensitivity, neurological degeneration etc.)

• Defect in transcription coupled repair (TCR)

• Defective 8-oxodG excision (50%)• Subtypes: CS-A, CS-B• Global genome repair (GGR) is

proficient

Cockayne syndrome

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• Lamin A mutation (nuclear envelope fragility)

• Primerily affects mesenchymal tissues• HGPS cells have decreased stress

resistence• Rapid progeria, premature death

Hutchinson-Guilford progeria syndrome

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DNA REPAIR

(limited synthesis:

small fragments) Cell cycle

arrest(Apoptosis) Mutations

Cancer and genetic diseases

Replication errors

X rays

UV light

Alkylating agents

Spontaneous reactions

Reactive oxygen species (ROS)

DNA damage: causes, results I

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Oxidative DNA damage• > 10,000 DNA lesions / cell / day• A variety of DNA damage types (> 50 types)• 5 distinctive groups

- Oxidized purines- Oxidized pyrimidines- Abasic sites- Single-strand breaks- Double-strand breaks

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Stochastic

Regulated

DNA damage: causes, results II

Mutations, epi-mutations

Altered regulatory circuits

DampenedGH/IGF axis

Cellular responses(apoptosis,

senescence)

Improved survival Tissue atrophy, lost regeneration

ExogenusMetabolism

DNA damage

Tissue/organ functional decline, degenerative or hyperplastic disease

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• Base excision repair (BER) is most important, subtypes: AP endonuclease or lyase repair

• Removal of oxidized purines (two types of lesions: 8-oxodG and formamido-pyrimidines)

• Removal of oxidized pyrimidines (strong block, strongly cytotoxic)

• Repair of abasic sites (most frequent) by AP endonucleases

Oxidative DNA damage repair types I

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• Repair of strand breaks (single-strand breaks occur 10x more frequently than doubles)

• Limited mitochondrial DNA repair (nuclear encoded proteins of OGG1, POLG)

• Nucleotide excision repair (NER) that is transcription-coupled repair of active genes

Oxidative DNA damage repair types II

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• Defect is lethal: APE1, FEN1, POLB, LIG1, LIG3, XRCC1

• Defect is viable: OGG1, NTHL1, MYH, ADPRT

• Severity not tested: NEIL1, 2, 3, TDG, SMUG1, APE2

Genes related to oxidative DNA damage repair

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• Elevated cancer frequencies• Werner syndrome (anti-recombinase)• Cockayne syndrome (TCR)• XPD and XPA (repair deficiency)• Base excision repair (BER) defect is

lethal• Back-up repair pathways

Oxidative DNA damage repair and aging

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• Depurination and depyrimidination• Deamination• Single-strand breaks• Spontaneous methylation• Glycation• Cross-linking

Non-oxidative DNA damage

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• Biosynthetic errors• Transcriptional errors• Translational errors• Racemization and isomerization• Deamidation (asparagine and

glutamine)• Reactive carbonyl groups (non-

oxidative)• Serine dephosphorylation

Non-oxidative protein damage