Manifestation of Novel Social Challenges of the European Union in the Teaching Material of Medical Biotechnology Master’s Programmes at the University of Pécs and at the University of Debrecen

Medical Biotechnology Master’s Programmes

at the University of Pécs and at the University of Debrecen

Identification number: TÁMOP-4.1.2-08/1/A-2009-0011

AGING AND GENE EXPRESSION –

ALTERATIONS OF THE GENOME DUE TO

AGING

Krisztián Kvell

Molecular and Clinical Basics of Gerontology – Lecture 22

at the University of Pécs and at the University of Debrecen

Identification number: TÁMOP-4.1.2-08/1/A-2009-0011

T T A

DNA

RNA template

Telomerase

Nucleotides

A

A U C C C A

Telomere sequence and

telomerase function

• 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

• 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

Telomere is repetitive DNA sequence Embyonic

stem cells

Adult stem cells

Telomere long

Telomere short Active

telomerase

Telomerase inactive or absent

A

A T C C C T

T A G G G

Changes in telomere length

Chromosome

Extending the length of a telomere

New DNA Short end of DNA

G

G T T A

A U C C C A A U C RNA template

T C C C A A T C C C A A

T T A G A G G G

Telomerase DNA polymerase

• Counteracting (oxidative) stress conditions

• Telomerase activity increases telomere length

• ALT: alternative telomere lengthening

Slowing, reversing telomere

shortening

Telomerase reactivation

Further evolution Loss of telomere function

Significance of telomere in cancer

Telomere lenght

Number of aberrations Genome instability

Normal tissue Hyperplasia Carcinoma in situ Telomere

crisis

Invasive cancer

• Soluble factors / cell non-autonomous spreading

• Pineal clock, role of melatonin

• Circadian clock mechanisms

• DNA methylation, acetylation, de-acetylation

Further clocks ticking

• Werner-syndrome

• Cockayne syndrome

• Hutchinson-Guilford progeria

• Xeroderma pigmentosum

Genomic instability in progeria types

• 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

• 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

• Lamin A mutation (nuclear envelope fragility)

• Primerily affects mesenchymal tissues

• HGPS cells have decreased stress resistence

• Rapid progeria, premature death

Hutchinson-Guilford progeria

syndrome

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

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

Stochastic

Regulated

DNA damage: causes, results II

Mutations, epi-mutations

Altered regulatory circuits Dampened

GH/IGF axis

Cellular responses (apoptosis, senescence)

Improved survival Tissue atrophy, lost regeneration

Exogenus Metabolism

DNA damage

Tissue/organ functional decline, degenerative or hyperplastic disease

• 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

• 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

• 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

• 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

aging

• Depurination and depyrimidination

• Deamination

• Single-strand breaks

• Spontaneous methylation

• Glycation

• Cross-linking

Non-oxidative DNA damage

• Biosynthetic errors

• Transcriptional errors

• Translational errors

• Racemization and isomerization

• Deamidation (asparagine and glutamine)

• Reactive carbonyl groups (non-oxidative)

• Serine dephosphorylation

Non-oxidative protein damage