Aging and immortal cells

1. Aging and immortal cells

2. Aging ?

3. Why do we get old ? What is aging ? • Aging - Phenotypic changes that occur over time due to limiting processes • Aging is a process that converts an optimally healthy, fit organism into a less healthy, less fit organism • Aging is a biological process and not a disease, per se • Are we programmed to die ?

4. Aging - features • Aging = reduced functional tissue • Aging = increased susceptibility to disease (age-related diseases) • Aging = decreased resistance to stress (physical and mental)

5. Mortality in Aging and Non-aging Systems aging system non-aging system Example: radioactive decay

6. Why do we age? Genes + Environment

7. Genes and Aging • Genes determine species-specific life span • Genes determine differences in aging among individuals within a species (differences in gene expression / polymorphisms)

8. Species-specific longevity genes • Flies (Drosophila melanogaster) • Mice • Humans • Turtles • Life spans from 2 weeks to 200 years

9. 50 Years 18 Months AGING in MICE AND MEN MICE HUMANS Fitness Disease (Cancer, osteoporosis, diabetes, etc.) AGE (log) Mice and Humans are >90% genetically similar!

10. Species-specific longevity genes What are the genes that determine why mice live <4 years, whereas humans live >100 years? Big pay-off, but complicated by development/evolution

11. Individual longevity genes Small pay-off, but possibly amenable to intervention (environment, life style, drugs??)

12. Environment and aging Present environment + Past environment

13. Present environment and Aging • Diet • Exercise • Stress

14. Diet and Aging • Food = simple molecules + oxygen • Oxygen (mitochondria) – energy + ROS • ROS = damaging by-products can modulate gene expression • Anti-oxidant defenses good, but not perfect (differ among species) • OPTIMAL food = less ROS, less damage • OPTIMAL food = longer lifespans!

15. Diet and Aging • C.elegans with mutations leading to increased SOD and catalase - doubles life span • Similar changes in Drosophila and yeasts

16. Exercise and aging • Exercise – greater fitness, healthier muscles • Exercise – protection from oxidative stress

17. Stress and aging • Physiological stress – hormonal changes • Physical stress – Eg. too much of exercise – increases ROS • Mental stress – impaired Cardiovascular function / reduced immune response and accelerated telomere shortening (eg. Parents who cared for a chronically ill child) - even perception of stress correlated

18. Past environment and aging • Genes evolve in response to environment (Key factor in aging)

19. Aging and past environment "Protected" Environment (climate control, biomedical intervention etc.) 100% SURVIVORS "Natural" Environment (hazards, climate, infection, etc.) HUMANS: 40 yrs 80 yrs AGE

20. Aging and past environment • Bad environment leads to accumulation of mutations that can persist • Keep the environment good – extend life spans • But it may take a really long time !

21. Factors leading to aging http://www.anti-aging.gr.jp/english/anti.phtml

22. Telomeres and Aging:Is there a connection?

23. What are telomeres? • Telomeres are… • Repetitive DNA sequences at the ends of all human chromosomes • They contain thousands of repeats of the six-nucleotide sequence, TTAGGG • In humans there are 46 chromosomes and thus 92 telomeres (one at each end)

24. Why are telomeres important? Telomeres allow cells to distinguish chromosomes ends from broken DNA Stop cell cycle! Repair or die!! Homologous recombination (error free, but need nearby homologue) Non-homologous end joining (any time, but error-prone)

25. What do telomeres do? • They protect the chromosomes. • They separate one chromosome from another in the DNA sequence • Without telomeres, the ends of the chromosomes would be "repaired", leading to chromosome fusion and massive genomic instability.

26. Telomeres… • Telomeres effectively "cap" the end of a chromosome in a manner similar to the way the plastic on the ends of our shoelaces "caps" and protects the shoelaces from unraveling. • Telomeric sequences shorten each time the DNA replicates.

27. The End Replication Problem: Telomeres shorten with each S phase 5' 3' 3' 5' 3' 5' 5' 5' 3' Ori DNA replication is bidirectional Polymerases move 5' to 3' Each round of DNA replication leaves 50-200 bp DNA unreplicated at the 3' end

28. Telomeres and aging • Telomeres are also thought to be the "clock" that regulates how many times an individual cell can divide. • Once the telomere shrinks to a certain level, the cell can no longer divide. Its metabolism slows down, it ages, and dies. • Healthy human cells are mortal because they can divide only a finite number of times, growing older each time they divide. Thus cells in an elderly person are much older than cells in an infant.

29. Telomere also provide a means for "counting" cell division: telomeres shorten with each cycle Telomeres shorten from 10-20 kb (germ line) to 3-5 kb after 50-60 doublings Cellular senescence is triggered when cells acquire one or a few critically short telomeres. 20 Normal Somatic Cells Telomere Length (humans) 10 (Telomerase Negative) Cellular (Replicative) Senescence Number of Doublings

30. Telomeres & Aging • It has been proposed that telomere shortening may be a molecular clock mechanism that counts the number of times a cell has divided and when telomeres are short, cellular senescence (growth arrest) occurs. • shortened telomeres in dividing cells are responsible for some of the changes we associate with normal aging.

31. What next? • So, scientists have determined that there is a direct connection between telomere length and aging. What was their next step?

32. What is telomerase? • Telomerase is an enzyme complex that has been referred to as a cellular immortalizing enzyme. • It stabilizes telomere length by adding hexameric (TTAGGG) repeats onto the telomeric ends of the chromosomes, thus compensating for the erosion of telomeres that occurs in its absence. • Cells in tissue culture with telomerase have extended the length of their telomeres – and can divide for 250 generations past the time they normally would stop dividing.

33. Telomerase activity • Most normal cells do not have this enzyme and thus they lose telomeres with each division. • High telomerase activity exists in germ cells, stem cells, epidermal skin cells, hair cells, and cancer cells.

34. Telomerase and cancer • Cancer cells do not age because they produce telomerase, which keeps the telomere intact. • There is experimental evidence from hundreds of independent laboratories that telomerase activity is present in almost all human tumors but not in tissues adjacent to the tumors.

35. Hayflick limit • The number of times normal cells divide before they stop dividing. • ? Telomere shortening

36. Werner syndrome Accelerated aging due to rapid telomere shortening

37. Possible interventions to delay aging • Stem cells • Anti-oxidants • Telomerase

38. Questions posed ? • Do mechanisms of aging work in a tissue specific manner ? • Is aging amenable to therapeutic intervention ? • Is therapeutic intervention advisable ?