L4, Damage Theories II

Question 1

Compare DNA, lipid, protein and AGE oxidation products -> relevance to biogerentology field?

Answer 1

• DNA damage: Long lasting but repairable. Can accumulate, particularly in mtDNA -> functional impact
• Lipid peroxidation products: Short lasting, good acute markers of redox state -> structural impact
• Protein carbonyls: Long lasting, repairable. Accumulate with age -> Structural AND functional impacts
• AGEs: Very long lasting and unrepairable. Accumulate with age

Question 2

Experimental evidence against natural DNA damage as a mechanism for aging (butterfly wasps):

Answer 2

• 1960s experiment using parasitic wasp of butterflies
• Habrobracon wasps can produce haploid or diploid males from same mother
• Study investigated lifespans of the two groups -> theoretically, the diploid would be less vulnerable to natural DNA damage
• X-irradiation did shorten lifespan of haploid more severely
• Natural conditions: same lifespan -> argument does not hold

Question 3

Drosophila study: temperature vs DR effects on mortality…

Answer 3

• Temperature: Decreasing temperature (27 to 18 degrees) lowered rate of aging (Gompertz G parameter)
• DR: Application of DR affected baseline risk of death (Gompertz A/intercept) -> delaying onset of age-associated mortality
• Results included simple differences in temp/DR, but also a switched condition in which the slop defaulted to that of the new condition mid experiment

Question 4

Experimental evidence for oxidation markers tracking aging rate:

Answer 4

• Investigations using GSA and MDAL did not track results previously observed for aging under temperature and DR shifts
• Suggesting they are not causing aging

Question 5

Experimental evidence for AGEs tracking aging rate:

Answer 5

• Similar temp and DR experiments as previously
• Changes in levels of AGEs appear to track mortality rate changes better than oxidised proteins (more permanent -> can’t easily revert to lower levels)
• Results are particularly apparent in temperature experiments
• Strong correlation demonstrated -> further evidence required for causation

Question 6

3 key predictions of FRTA:

Answer 6

1. Resistance to oxidative stress should correlate with longevity
2. Overexpression of antioxidant systems should increase lifespan
3. Long-lived animals should exhibit less oxidative damage and have enhanced antioxidant systems compared to short-lived animals of the same chronological age

Question 7

Study into oxidative stress resistance and lifespan (worms):

Answer 7

• Nematode worm study using ‘death fluorescence’ to mark exact time of death regardless of movement etc
• Subjects had different phenotypes with varying resistance to oxidative stress and heat shock
• Severe oxidative stress resistance did not correlate with lifespan
• Heat shock resistance does

Question 8

Initial results of overexpression of SOD and catalase in flies: (1990s)

Answer 8

• Landmark/influential 1990s study using isogenic Drosophila melanogaster
• Investigated if antioxidant enzyme overexpression extended lifespan (i.e. FRTA)
• Overexpression of these enzymes was found to extend the lifespan and slow down various age-related biochemical and functional alterations
• Previous studies into these enzymes alone showed only minimal improvements in lifespan -> it is the antioxidant system in concert which was important here for extending lifespan
• Control strain has a relatively short lifespan
• Key take-aways: Less carbonyls and longer life, but higher metabolic potential

Question 9

Further study into antioxidant overexpression in flies: (2003)

Answer 9

• Later study (2003) than landmark 1990s study; attempted to replicate -> debunked some of the wider conclusions
• Found the lifetime-extending effect of these enzymes to only be impactful in already short-lived strains
• ‘Results suggest that bolstering antioxidant defences is only effective in compromised genetic backgrounds’

Question 10

Study into overexpression of catalase in mice: (2005)

Answer 10

• Aiming to look at effect of ROS in mammals -> transgenic mice for human catalase, targeted to various organelles
• Median and maximum lifespans were maximally increased in MCAT (mitochondrial targeting enzyme) animals
• Cardiac pathology and cataract development were delayed, oxidative damage was reduced, hydrogen peroxide production attenuated
• Development of mitochondrial deletions was reduced
• Supports FRTA; reinforces importance of mitochondria as a source of ROS

Question 11

Briefly summarise results of 2012 study into antioxidant systems in birds:

Answer 11

• The pronounced longevity of long-lived parrots vs short lived quails appears to be independent of their antioxidant mechanisms and their accumulation of oxidative damage
• Study encompassed levels of oxidative damage. expression of various enzymes involved and markers of DNA/lipid/protein oxidation

Question 12

Effects of aging and reproduction on protein quality control in soma and gametes of Drosophila Melanogaster (2012):

Answer 12

• Investigating levels of protein carbonylation and HNE in soma and germline of young vs old subjects
• Showed consistent ‘quality control’ in eggs but not in soma (egg oxidative damage remained relatively low in young vs old, whereas soma damage started high and increased over lifetime)
• Also looked at head vs thorax vs abdomen tissues (abdomen containing lots of eggs -> representing germline). Discovered the abdomen alone had high levels of chaperone proteins, heat shock proteins, proteasome
• -> Dramatically increased protein quality control
• Consider DSTA -> Would devoting energy to soma be energetically and/or evolutionarily wasteful?