Cell Death and Neurotrophic factors Flashcards Preview

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Flashcards in Cell Death and Neurotrophic factors Deck (38)
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1
Q

how can cells undergoing apoptosis be distinguished?

A

their nucleus becomes very dark and enlarged as the chromatin condenses and cytoplasmic blebbing

2
Q

what are the two ways in which cell death can occur

A

necrosis or apoptosis

3
Q

how is apoptosis carried out?

A

activated of caspases which are proteolytic enzymes that break down the nuclear lamina and cytoskeleton so that the cell can be cleared safely by macrophages- the DNA is also fragmented

4
Q

describe the process of apoptosis molecularly

A
  1. there is an influx of ions into the mitochondria
  2. release of cytochrome C which binds to Apaf 1
  3. activation of Caspase 9
  4. Activation of Caspase 3 via cleavage
  5. caspase 3 degrades cellular components
5
Q

what things normally stimulate cell death?

A
  • a lack of growth factors

- stimulation of apoptosis pathway

6
Q

what happens when you KO caspase 9 in the mouse?

A

you get an overgrown brain

7
Q

what receptor normally stimulates apoptosis when bound?

A

Fas or TNFH

8
Q

describe an experiment which looked at the effect of removing or adding a limb bud to an embryo… what did this show?

A

if can use a strain such as DiI which will stain the entire neuron. Normally you see that the motor neurons are all present in the ventral part of the cord. You can then use one limb as a control and the one on the opposite side to experiment. You can remove a limb bud and you see that the motor neuron number decreases. you can also add a limb bud and you will see that you get more motor neurons in the ventral region.
- This shows that the number of motor neurons is not set and can vary depending on the presence or absence of a limb- maybe the limb sends a signal

9
Q

how was it shown that cell death of neurons varies according to whether along the spine the DRG is? what happens when you then ablate a limb

A

if you measure the DRG death rate in neurons you find that there is less death in the DRG that innervate limb buds that in other regions. This suggests that “all DRG neurons are created equally” and cell death occurs depending on where the DGR is situated. This is further supported by the fact that if you ablate a limb then the segment gets just as much cell death as the non limb DRGS- so the death rate is depending on the limb

10
Q

what is the neurotrophic hypothesis?

A

this is the hypothesis that neurons compete for a limited amount of neurotrophic factor that is produced by their target. Those neurons that receive sufficient ‘trophic support’ survive and others die. Survival requires a retrograde signal from the periphery to the cell body

11
Q

describe how the NGF was discovered.

A
  • they implanted tumour cells into the limb bud. They found that this promoted the survival of sensory and sympathetic neurones. There was a huge growth in the ganglia. This showed that there was something in the tumour that could promote survival.
  • they then placed tumour cells on on the chorioallantoic membrane promoted survival of sensory and sympathetic neurons. This shows that the sarcoma -derived surival factor is diffusible!
  • they then cultured DRG on the same culture that a mouse sarcoma was cultured on and saw it promoted growth
  • for some reason they thought it was nucleic acid and they knew that snake snake venom phosphodiesterase could break down nucleotides so they added this- saw that it still grew so then they tried venom alone and it worked
  • they purified and found NGF!
12
Q

how did they investigate whether NGF promoted growth or just survival?

A

they used antibodies against NGF and found that there was reduced growth and cell survival in the DRG cultured

13
Q

how did they investigate that NGF was a ligand?

A

they knew that a good ligand has a low effect at low levels and a high affect at high levels so they did this with NGF and looked at the survival rate and found it was dose dependent and plateaued.

14
Q

how did they show that NGF worked via retrograde signalling?

A

they used a culture chamber that allows neuronal cell bodies to be exposed to different environments. they put NGF with the peripheral sons and nothing in the cell body chamber- the survival and growth was improved- not when you put antibody in

15
Q

how did they test whether NGF also works on type of neurons other than motor neurons? what did this mean?

A

they carried out the same culture experiments with sympathetic neurons and sensory neurons but not on any others including spinal motor neurons- this means that NGF can’t be the whole story, there must be more

16
Q

what are the 5 main neurotrophins?

A

nerve growth factor, brain derived growth factor, neurotrophin-2 and NT-4/5

17
Q

what does NGF promote the survival and growth of?

A

nociceptor afferents

18
Q

what does BDNF promote the survival and growth of?

A

fine touch afferents

19
Q

what does NT4 promote the survival and growth of?

A

hair follicle afferents

20
Q

what does NT3 promote the survival and growth of?

A

spindle afferents

21
Q

do neurons change which growth factor they depend on? give an example

A

yes, over time, the trigeminal originally depend on BDNF or Nt-3 early in development but then depend on NGF

22
Q

what receptor does NGF bind to ?

A

TrkA

23
Q

what receptor do BDNF and NT-4/5 bind to ?

A

TrkB

24
Q

what receptor does NT-3 bind to ?

A

TrkC and maybe TrkB

25
Q

what i the NTR p75 receptor?

A

it is a receptor that has an 1000x lower affinity for NGF compared to TrkA
- NGF signalling via TrkA is potentiated by p75

26
Q

what does NGF signalling p75 in the absence of TrkA promote?

A

apoptosis

27
Q

how do the Trk receptors generally work?

A

they bind their ligand, they dimerise and autophosphorylate each other. Then adaptor proteins bind to phosphotyrosine and activate pathways via PI3K, Ras-MAPK, and phospholipase C-gamma

28
Q

what is the PI3K pathway involved in?

A

survival

29
Q

what is the Ras-MAPK pathway involved in?

A

differentiation and axonal and dendritic growth

30
Q

what is the PLC gamma pathway involved in?

A

synapse formation

31
Q

how can the activation of PI3K prevent the appoptosis pathway?

A
  1. activation of TrkA by NGF
  2. activation of PI3K
  3. Activation of AKt
  4. Phosphorylation of Bad
  5. Phosphorylation of Bad allows it to be sequestered by 14-3-3
  6. sequestration of Bas allows Bcl-2 and Bcl-Xl to keep Bax ion channels closed on the mitochondria- cell survives
32
Q

what are the sources of trophic factors?

A

target derived, ECM, non neuronal derived, CNS glial derived, Afferent derived,
autocrine/ paracrine derived, systemically derived

33
Q

approx how many motor neurons generated in the spinal cord die during embryonic development?

A

half

34
Q

what neurotrophic factor supports proprioceptive sensory neurons?

A

NT-3

35
Q

which neurotrophic factors supports nociceptive neurons?

A

NGF

36
Q

which trophic factor supports mechanoceptors that innervate merger cells?

A

NT-3

37
Q

what trophic factors support nerves that innervate hair follicles?

A

NT4 and NT5

38
Q

describe 2 other apposite pathways other than mitochondria/ ApoE/ Caspase 9

A

bacl- bax, bak- then triggers mito pathway. DNA damage- p53- puma,nova,bcd-2,bcd-xl, bad,back, mitochondria
( growth factor receptors activate PI3K and AKT which inhibits Bacl