Ageing Flashcards
What is ageing by definition?
The progressive, irreversible decline in organismal performance
What occurs in the organism as a result of ageing?
Failure of multiple systems
What are the main causes of death after 65 years old in the UK?
- Cancer
- Heart and lung problems
- Alzheimers
- Parkinsons
Can we prevent ageing?
Possible if we know the factors that influence ageing
What are the factors that influence ageing?
1) GENETICS (internal factors)
2) ENVIRONMENT (external factors)
What are the genetic factors leading to ageing?
Genotype at BIRTH
Accumulation of mutations with age
What are the environmental factors leading to ageing?
Diet
Lifestyle
Exposure to various external factors
What can/cannot be studied in model organisms in regards to ageing?
Can:
- GENETICS of ageing
Can’t:
- Environmental factors
What must model organisms be to study ageing?
- Small, easy to culture
- Short life span
- Genetically tractable
- Can be kept in a controllable environment
Why must model organisms be kept in a controllable environment?
To ensure that changes are dependant on GENETICS and not environment
What is the lifespan of c.elegans?
Drosophila?
Mouse?
Weeks
Months
Years
How can we measure ageing?
No direct method to measure ageing
Instead, measure age at DEATH
Demographic approached - large cohorts of identical animals –> build a survival curve
What can be identified using a survival curve?
Medial lifespan (on average how long a particular GENETIC COMBINATION lives)
What does the survival curve of drosophila show?
What other organisms show this?
Females live longer than males
Humans also show this
What makes drosophila a powerful tool to find the genes regulating LIFE SPAN?
- Short-life span
- Can undergo genetic screens
What did screens of the drosophila show was important in ageing?
How?
The INSULIN/IGF-1 PATHWAY is important in ageing
As well as ageing, what does the insulin pathway impact on?(2)
1) Has a role in the regulation of brain function
2) Regulates human body homeostasis - important during development
What is the role of the insulin hormone?
Promotes the uptake of glucose from the blood for STORGAE
eIn this course, where has insulin been met before?
Energy balance
What is the insulin signalling pathway?
1) Insulin binds to insulin receptor
2) Intracellular cascade - PI3 –> Akt
3) Represses the function of FOXO AND promotes the function of S6K (through mTOR)
What is the normal function of FOXO?
INHIBITION of cell PROLIFERATION and NUMBER
What is the normal function of s6K?
INCREASE in cell SIZE (growth)
What did the first indication that the insulin pathway is involved in ageing?
What is thus protein?
With the chico protein
An insulin receptor substrate - functions in the insulin pathway in drosophila
What occurs in HETEROZYGOUS drosophila with chico mutant?
Why?
LONG lived (both males and females)
Pathway is REDUCED but not COMPLETELY ABOLISHED
–> longevity
What occurs in HOMOZYGOUS drosophila with chico mutant?
Why?
LETHAL
COMPLETELY abolishes the insulin pathway
Is the insulin/IGF-1 pathway conserved?
YES
HIGHLY conserved
What was shown after the original discovery of chico in longevity in drosophila?
Shown in other animals to have the SAME effect
Shown that other components of the pathway have the same roles
What are components that ACTIVATE the insulin pathway?
What do HETERO mutations in these components show?
Insulin receptor
Insulin
PI3K
mTOR
Mutations –> promote longevity
What are components that INACTIVATE the insulin pathway?
What do OVEREXPRESSION in these components show?
PTEN
FOXO
Over expression –> reduce activity of the pathway –> promote longevity
How does a reduction in the insulin pathway increase longevity? (2)
How?
On the whole organism level:
1) Increases autophagy and DNA repair –> less accumulation of mutation and less senesence
2) Reduction in oxidative stress
- By inhibiting mTOR that normally acts to increase cell size (by blocking autophagy) and by inhibiting the inhibition FOXO (now activated) that acts to REDUCE cell proliferation (ROS involved in cell proliferation)
–> Ultimately increasing health and longevity
What does Methuselah do?
A gene that encodes the receptor that triggers insulin release –> activates the insulin pathway in response to NUTRIENTS
What happens the methuselah mutants?
Long lived
What does a peptide antagonist of methuselah do?
On the other hand?
EXTENDS life-span
BUT:
- Functional abilities are BELOW the CONTROL level at old ages (flies live longer but they are less healthy and perform WORSE when they are old compared to control)
- Control flies live shorter lives but they are HEALTHIER - more active, longer flight duration
What impact does dietary restriction have on life-span? What effect does this show?
On the other hand?
MODEST dietary restriction (reduced nutrient intake –> extends lifespan)
Shows ENVIRONMENTAL EFFECTS
But if food concentration is TOO LOW –> flies die
What is another way to measure longevity of life?
What does this show?
The PROBABILITY of death at each age (taken from the survival curve)
Shows:
- Probability of death increases exponentially with age
What can be produced from the probability curve?
What does this show?
Plot on a log scale:
- Produces a straight line
Shows:
- Probability of death is LINEAR with age
What were the experiments performed by scientists to see if dietary restriction can extend life when applied at a particular point or throughout life?
Conclusion:
Fully fed flies:
- Higher mortality rate than dietary restricted flies
- Switch flies to dietary restriction @ day 14 or day 22
SAW: mortality rate reduced dramatically to the level the same as flies that were kept on dietary restriction throughout their lifetime
Then - reverse experiment:
- Switch dietary restriction to fully fed at day 14 or day 22
SAW:
- Flies started to die as quickly as flies that were kept on fully fed diet throughout life
CONCLUSION:
- DR reduces mortality risk at any time of life
When is middle aged for a fly?
22 days
What is CALORIE?
Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy
Where are insulin receptors found?
In the hypothalamus
As well as insulin, what acts on the insulin receptors?
What happens when this binds to insulin receptors in the hypothamus? (2)
LEPTIN:
- Regulates food hunger, food intake and feeding behaviour
- INDIRECTLY regulates INSULIN SECRETION
How does insulin act in the brain?
Acts in the hypothalamus to control glucose metabolism
What does the evidence show that is regulating lifespan?
Insulin receptors in the hypothlamus
What is IGF-1?
Insulin Growth Factor-1
What is IGF-1 production simulated by?
Hypothalamus GHRH (growth hormone releasing hormone)
Why is Alzheimer’s do demanding?
- Increasing number of people diagnosed
- Large strain on the economy
What occurs in Alzheimer’s? (2)
1) Neurodegeneration, cell death, tissue atrophy –> impairs cognitive function
2) Accumulation of beta-amyloid peptides in the cells of the brain –> over expression in drosophila is neurotoxicity
How does known information of Alzheimer’s be used to promote healthy ageing?
Can screen for genes that potentially REDUCE neurotoxicity/beta-amyloid peptides –> used for drug targets?
How can over express a gene using the UAS/Gal4 system?
How is this used to study ageing?
Fly 1:
- Sequence coding for Gal4 under the regulation of a promoter expressed in a particular TISSUE or a particular TIME (eg. brain)
Fly 2:
- UAS (upstream activating sequence promoter) fused to the coding system of interest OR an interfering construct targeting a gene of interest
CROSS FLIES TOGETHER:
- Gal4 produces where the promoter is expressed (specific tissue/time)
- Gal4 binds to the UAS promoter –> produces the gene of interest
Study ageing:
- Can over express beta-amyloid peptide in SPECIFIC NEURONAL CELLS
- THEN, can screen for genes that increase life span or prevent the degeneration of these neurons
What is used to score the effect of the genes that increase life span/prevent neurodegeneration? Why?
Drosophila eye
Easy to score
What is the structure of the drosophila eye?
How can this model be scored easily?
- Compound structure of ~750 individual units (ommatidia)
- Each ommatidia - has 8 photoreceptors
- Photosensitive membrane in each photoreceptor - rhabdomere
Scored easily:
- Can shine red light on the flies - see the photoreceptors under the microscope without needing to dissect/fix/prepare tissue
- Can COUNT how many photoreceptors/neurons are remaining
What is the difference between WT and the disease model (when over express beta-amyloid peptide)?
Disease model:
- Over-half of the photoreceptors are GONE
What is IDE?
What does it do?
Insulin degrading enzyme:
- Evolutionally conserved metalloendopeptidase
- Binds to insulin molecules before they bind to the receptor and REDUCES insulin pathway signalling
Where is IDE in the body?
Expressed by cells and secreted extracellularily
How does IDE interact with beta-amyloid peptidase?
Over-expression of beta-amyloid peptidase induces neurotoxicity (shown by reduction in photoR/neurons in the drosophila eye)
IDE reduces this induced neurotoxicity and increases lifespan (but not at long as WT flies)
Describe the experiment with Beta-amyloid peptide
Beta-amyloid overexpressed specifically in all fly neurons using elav
At the same time, elav expresses GFP
–> Reduces the lifespan
What is elav?
The promoter which expressed GAL4 in all neuronal cells
What happens when express beta-amyloid peptide with HUMAN IDE in flies?
What does this suggest?
REDUCES the lifespan of the flies to their counterparts
–> prevents neurodegeneration and increases lifespan
Suggests:
- Decrease of insulin signalling potentially decrease Alzheimers?
What is the role of the hypothalamus?
Important for regulating insulin production and calorie intake
Can speculate hypothalamic function is important in the onset and progression of Alzhemier’s
What mediates the increase in lifespan by DR in the drosophila?
Nutrient sensing pathways (insulin/IGF1 pathway) and TOR pathway
How is the mTOR pathway activated?
How is it inhibited?
What does this lead to?How?
By nutrients
Inhibited by RAPAMYCIN Extension of life span due to: - Autophagy and DNA repair OR - Reduction of cancer??
What is the action of sirtuins?
What does this cause?
ACTIVATE FOXO
Increase longevity
SO, what leads to INCREASE in longevity?
INCREASE IN:
- FOXO
- Sirtuins
- PTEN
DECREASE (NOT COMPLETE ABLATION OF) IN:
- mTOR and S6K
- Insulin
- Insulin R
- Chico
- Mth gene (receptor that results in insulin release in response to nutrients)
What is chico?
An insulin receptor substrate - functions in the insulin pathway in drosophila
Why does this reduction in insulin signalling increase longevity?
Drosophila go into a reproductive diapause
