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