18. ageing biology 4 Flashcards
1
Q
what types of yeast can we used to study ageing? and what are the specifically useful to study?
A
budding yeast
>central biochemistry behind nutrient sensing
2
Q
what are the pros of using budding yeast?(4)
A
- small sequenced genome
- cheep
- quick
- easy to genetically manipulate
3
Q
why are results obtained from budding yeast useful to us?
A
many gene orthologues in humans
4
Q
discuss budding yeast life span
A
they have a finite replicative capacity - their replicative lifespan
5
Q
what is CLS?
A
the chronological lifespan of budding yeast - this is how long they can survive in a non-diving state
6
Q
describe old budding yeast (4)
A
- they are larger
- cell cycle and proteins synthesis slower
- cells surface looks loose and wrinkled
- show apoptotic markers
7
Q
what can use suggest when looking at irregular less plump yeast?
A
they are accumulating more dysfunctional proteins/their genome is stressed
8
Q
what can increase lifespan in yeast?
A
dietary restriction - reduced glucose and/or amino acids in their broth
9
Q
when calorie restriction was done on yeast, what % were their calories reduced by?
A
30/40%
10
Q
what are sirtuins?
A
they act as nutrients sensors that are regulated by NAD+
>they regulate many aspects of biology
11
Q
what functions can sirtuins have?
A
> deacetylate histones and compact DNA
>deacetylate TFs and regulate gene expression
12
Q
what does SIRT1 signalling do?
A
it leads to increase insulin secretion form the pancreas
13
Q
SIRT1 may increase senescence and apoptosis, but what may it also increase?
A
resilience and autophagy
14
Q
SIRTs can regulate TFs and gene expression, what sort of processes can these regulate?
A
- glucose production in the liver
- fat metabolism
- angiogenesis
- neuronal development
- resistance to neurodegeneration
- increased insulin secretion from pancreas
15
Q
what affects does SIRT1 have on ageing? and what implication does this have on therapeutics?
A
+ and - effects
>we may need to look at tissue specific regulation for preventing ageing phenotype
16
Q
what happen when there is lots of nutrients available?
A
- high metabolism, less NAD+
- sir2 inactive
- normal reproductive rate
- normal lifespan
17
Q
what happen when there is low nutrients available?
A
- low metabolism, high NAD+
- SIr2 active
- stress response - it is good to stress you tissue slightly
- reduced fertility
- longer lifespan
18
Q
what choices can be made in increase lifespan?
A
not to reproduce and have non-essential activity
19
Q
how many SIRTs are there in mammals?
A
7
20
Q
what processes do SIRTs influence? (7) (note: they have different effects in different tissues)
A
- senescence
- stem cells maintenance
- DNA damage repair
- metabolic regulation
- tumourigenesis
- neurogenesis
- inflammation
21
Q
what genes was identified in yeast when they were looking for genes of longevity and what does it do?
A
TOR - serine threonine kinase
high nutrients = high activity
inhibits stress response
regulates cell growth and proliferation
22
Q
what nutrients is TOR activated in response to?
A
oxygen, ATP, glucose, insulin and cytokines
23
Q
what does decreased TOR activity in yeast lead to?
A
increases RLS and CLS
24
Q
what happens when you starve cells and TOR activity is reduced?
A
stress response factors enter the nucleus
25
if signalling from mit to nucleus is reduced due to mit dysfunction, what is seen in yeast?
reduced RLS
26
what represses autophagy and what affect does this have on yeast?
TOR
| in decreased CLS
27
what two things can increase yeast lifespan? and what does this link to? and what is this conserved in? and how are they different?
TOR inhibition
Sir overexpression
>the most robust way to increase lifespan is calorie restriction
> conserved in worms, flies and mammals >they are unicellular, short lived, different DNA modification, no telomeres shortening
28
which second model animal shows functional senescence?
Drosophila e.g. heart, learn less well, explore less
29
how are Drosophila similar to us?
- they have gene structure
- they have kidney like structures
- neurons can develop protein aggregates
30
stress resistant Drosophila mutants live...
longer
31
what had CR and less reproduction shown in Drosophila?
increased lifespan
32
what has also been seen to reduced flies lifespan?
reducing insulin signalling
33
describe C elegans (4)
- transparent
- 1 mm
- cheap
- dead if stop moving
- sequenced genome - orthologues but lack Shh
34
what is seen in old worms? (3)
muscle dystrophy, reduced skin elasticity, venerable to infection
>they show signs of ageing
35
how long does it take for a C elegan to go from egg to adult?
4 days
36
how many stages are there in the laval development on C elgans?
4 stages
37
what happens when C elegans are starved in the 3rd laval stage?
they can survive for months without food
they have low metabolism
limited protein synthesis
survive of fat stores
38
how can genes be KO in C elegans?
feed them bacteria expressing RNAi
39
how many genes have shown to regulate lifespan in C elgans?
300+
40
what are the major pathways in regulating C elegans lifespan?
insulin like signalling - central way of monitoring nutrients availability
germline signalling
41
name the 1 insulin like receptor in C elegan and what does this receptor bind?
daf2
| >this bind insulin and IGF1 with different dynamics
42
what happens in C elegans when nutrients is low?
daf16 enters the nucleus as it is not P - this is part of the stress response
43
what happens when daf2 is activated?
there is a signalling pathways that results in activated AKT, this P Daf16, meaning it cannot enter the nucleus
44
what is daf16?
a TF
>represses growth and reproduction genes
>increases expression of genes for stress defence and altered metabolism
45
in yeast, C. elegans, drosophila, mammals: mutations in what lead to increased lifespan?
mutations that lower glucose or insulin signalling
46
what does nutrients excess cause?
>reduced lifespan
>obesity
>metabolic problems
47
nutrients sensing is an important regulator of ageing, what decision do cells make in regard to this?
whether to be active and reproduce or to not be very active
48
when nutrients receptor on yeast is activated, what happens?
kinases phosphorylate and inactivate transcription factors by excluding them from the nucleus
>this down regulates genes involved in stress response
49
what is downstream of the nutrient receptor in yeast and what happens when this is KO?
Ras
CLS increased by 2 times
by allowing transcription of stress response genes
50
in addition to allowing transcription of stress response genes, what else can reducing nutrient signalling do?
more glycerol leads to increased antioxidant activity - nutrient sensing and ROS can be linked
51
what can low glucose also stop? and what choice is this?
cell cycle - the growth vs anti-ageing choice
52
how much longer lived are daf2 mutants and what do they also show?
60-100% longer lived
| resistant to behavioural decline
53
what genes are daf16 involved in?
ROS scavengers
heat shock proteins
change metabolism - switches to hypometabolic state and start storing excess nutrients as fats and glycogen
54
what are heat shock proteins?
and folding of proteins, under stressful conditions, these are upregulated to protect and stabilise unfolded proteins, this gives the cell time to repair and re-synthesise damaged proteins
55
what can reducing the nutrient signalling pathway do in terms of immunity and senescence?
also boosts innate immunity and reduces cell senescence
56
how many ligands are there for the Drosophila sensing receptor? and what do they all diverge onto?
7
| >dFOXO
57
what happens when you mutate drosophila nutrient signalling receptor? (4)
longer life
reduced cardiac ageing
store nutrients
upregulate SOD
58
what happens when dFOXO is upregulated? and what does this have similar affect to?
longer life
| >KO the players in the pathway that reduced nutrient signalling
59
why is nutrient sensing more complex in mammals?
we have more signals and more forms of the receptor
| >there are three receptors in mice - they bind different proteins but share much of the same downstream signalling
60
what is insulin level a read out of?
nutritional state of the whole organism
61
what do insulin receptors converge on?
four Forkhead TFs (FOXO 1 3 4 6)
62
nutrient signalling is conserved between what?
yeast, worms, flies and mice
63
why is less known about human nutrient signalling?
not many complete body assays have been done in mammals/humans
64
stress may be due to reduction in nutrients, what does this lead to in humans?
```
FOXO enters the nucleus
>inhibits cell cycle
>regulates metabolism
>resists further stress
i.e. help contribute to resilience
```
65
what is necessary for the proliferation and self-renewal of NSC and what happens when this is reduced? why is this?
FOXO
NSC are depleted
>FOXO maintains self-renewal and constrains proliferation
66
what happens in brains of FOXO deficient mice?
they are initially larger, this is followed by decline in NSC pool and neurogenesis in the adult brain
67
what happens when nutrients are decreased in mammals? (3)
>less reproduction
>more stress response
>slower aging process
68
why does daf16 increase preserve post mitotic tissue?
by altering metabolism and increasing stress resistance
| >this increases lifespan of worm
69
FOXO increases self-renewal in stem cells, what does this mean in terms of HSC and NSC? what might FOXO increase in general?
>HSC decrease in ROS
>NSC decrease in ROS, altered metabolism, decreased Wnt signalling and altered cell cycle regulation
>tissue repair and lifespan
70
how does the cell decide whether to calm down metabolism or go ahead as if it has lots of nutrients?
FOXO and TCF mediated gene expression both compete for limited pool of beta catenin.
>during ageing and oxidative stress, production of ROS leads to increased FOXO mediated gene expression
>when nutrient signalling is present, FOXO is excluded from the nucleus and Wnt signalling can use beta catenin
>nutrient signalling also enhances nuclear beta catenin
71
what is a robust way to improve health of tissue?
calorie restriction
72
what is seen in IGFR+/- mice?
only females are longer lived
73
what might explain gender specific responses?
- due to the protective effects of oestrogen
74
why must studies on nutrient signalling be done on multiple strains? and what is this most important in?
there is variation between strains/genetic backgrounds
| >in subtle neurological disorders – different strains can really effect responses
75
what is seen when the nutrient signalling receptor is KO in mice?
would expect tissue to be resilient
>but lack of insulin signalling has knock on effects
>much sorter lives due to excessive keto acids in their blood
76
what affect can the dysregulation of insulin signalling in humans have?
T2D and cancer
77
we would expect that disrupting insulin signalling would have beneficial ageing affects, but this is not always the case, what implication does this have on therapy? give an example
developing tissue specific treatments/tissue specific restriction/modulation of insulin
>adipose tissue is very sensitive to insulin signalling. people trying to tackle obesity and diabetes are looking at ways to modulate insulin signalling in adipose tissue
78
what happens when insulin receptor is KO in neurones? and what does this mean in terms of therapy?
>mice were overweight and insulin resistant
but lifespan extended
>we need to decide if these side effects are worth tolerating or can be corrected
79
what happens when insulin receptors are KO in fat tissue?
>longer life
| >leaner and have increases insulin sensitivity
80
what was seen when the pituitary gland was removed from rats and what does this suggest?
they lived longer but the mice was smaller
| >growth hormone may be a factor in the ageing process - if you don't grow you might be more resilient to stress
81
in addition to growth, what does GH also stimulate?
Igf-1 release from liver
82
Ames dwarf mice, are small and live longer, why is this?
mutation in prop1 - this affects pituitary gland differentiation and so they have no GH in circulation and no plasma Igf1
83
name another mouse with similar phenotypes of Ames dwarf mice and what mutation is causing this?
Snell dwarf mice
mutations in Pit1 (downstream of Prop1) - this affects pituitary gland differentiation and so they have no GH in circulation and no plasma Igf1
84
what do Ames dwarf mice and Snell dwarf mice suggest?
maybe small size and reduced growth hormone may be useful in prolonging lifespan
85
what does reduced GH lead to in mice? (7)
1. small size
2. longer life
3. reduces insulin
4. increased insulin sensitivity
5. reduced fertility
6. reduces anabolism
7. reduces ROS
86
what happens to GH and IGF1 as we age? and what does this lead to?
they fall and lead to
>muscle weakness
>changes in body fat (similar to GH deficiency)
87
what can increase muscle mass and reduce fat in old people? and what does this suggest?
GH treatment
| >GH might rejuvenate
88
statically studies have shown what about reducing GH and Igf1?
there is no lifespan effects
89
what was concluded from GH/igf-1 signalling studies in humans?
more GH/igf-1 signalling can prevent some ageing symptoms but not increase lifespan
90
what is dietary restriction?
reduction in one/total nutrient level (no malnutrition)
| - generally calorie restriction
91
how can calorie restriction of 30-40% in mice affect lifespan? and does this have the same affect in most species?
extends lifespan by up to 50%
| >yes, most but not all species
92
why might we have evolved CR signalling?
to resist molecular stress/cell stress during periods of starvation
93
what evidence is there that TOR is involved in DR signalling?
- TOR inhibition mimics DR and prolong life
| - TOR mutants are not further affected by DR
94
how does TOR regulate translation?
upregulates ribosomal subunit and inhibits translation of its inhibitor
95
what does high metabolic rate mean? and what therapeutic idea stems from this?
>more proteins
>more organelles
>more leaking ETC
= the idea of translation inhibitors which might dampen down translation and reduce the effects of ageing
96
what two things are reduced during DR? and what question can be asked from this?
TOR activity
| translation - is decreased translation necessary for lifespan extension?
97
human trials looking at the effect on CR took place in 2007. they lasted for 6 months. what was observed and what were the limitations?
>muscle punch biopsy showed upregulation of SIRT1
>increased mit number
>reduced DNA damage
- this study was done on young not obese people for only 6 months
98
are anti-ageing pathways linear? and what does this mean?
no, there is cross talk between pathways
| >this means there is not one drugable target
99
what might longevity be a side effect of? what might also be affecting this?
CR survival mechanism
>other stresses: temperature, reproductive signals, respiration and translation
>cells is monitoring other stresses not just at the nutrients levels, they will all be feeding into these pathways
100
name 6 things that happen in a low nutrients response
stopping cell division, using energy stores, reducing translation, up regulating chaperones, increasing autophagy, reducing fertility
