Autophagy

Question 1

What is Autophagy?

Answer 1

A mechanism to digest intracellular material to recycle/degrade etc.

Question 2

Name some processes that require cell degradation

Answer 2

Homeostasis
Removing damaged components
Signalling
Recycling nutrients
Reprogramming cells (differentiation)

Question 3

What is a proteasome?

Answer 3

A complex of proteinases involved in breaking down selected intracellular proteins

Question 4

How does a proteasome work?

Answer 4

• Proteins targeted for proteolysis are marked with ubiquitin
• They are then unfolded and broken down into smaller peptides
  -Basically shredded

Question 5

What is macroautophagy?

Answer 5

Cargo in an isolated vehicle fuses with the lysosome to get chopped up, can remove whole organelles

Question 6

What is Chaperone-mediated autophagy?

Answer 6

Individual target proteins recognised by receptor and fed into lysosomes where they get digested

Question 7

What is microautophagy?

Answer 7

Lysosome has a little invagination which can extend around and take in small particles to be digested

Question 8

What is the role of macro autophagy in starvation?

Answer 8

Upregulated under starvation
Causes non-selective bulk degradation of the cytosol to gain nutrients
Cells get smaller because they are eating up themselves and using it to generate energy to stay alive, acc helps prolong the cell life as without this they would die within 2-3 days

Question 9

How do tumours use autophagy?

Answer 9

Use it to enhance growth
Tumours have limited vasculature so they have very poor access to nutrients and need autophagy to survive

Question 10

How is autophagy relevant in cellular remodelling?

Answer 10

Autophagy is the only mechanism to degrade organelles making it essential to form some specific cell types

Question 11

Give some examples of how autophagy is used in cell remodelling

Answer 11

-Red blood cells autophagy organelles such as mitochondria to make a mature, functioning red blood cells
-Mitochondria from the sperm also have to undergo autophagy as mitochondria is only maternal in the body

Question 12

How is autophagy relevant in removing damaged components?

Answer 12

Long-lived or highly metabolic cells such as neurons and muscle are the most susceptible
Protects from ageing and muscular dystrophhy

Question 13

Give an example of removing damaged components using macroautophagy

Answer 13

When we exercise our bodies are getting fitter as they are responding to the damage we do to the tissue, autophagy removes the damaged tissue so it can generate new ones

Question 14

Can autophagy make you live longer?

Answer 14

Can help elevate your repair pathways and help keep tissues healthier for longer

Question 15

What is the dietary restriction hypothesis?

Answer 15

Dietary restriction hypothesis says that starvation and exercise can lead to more autophagy and therefore more damage repair

Question 16

How is autophagy relevant in killing intracellular pathogens?

Answer 16

Pathogens can escape into the cytoplasm such as salmonella
Beneficial for the pathogen as once inside the cytoplasm they can use nutrients for survival and are protected from the immune system
Autophagy is used to capture them inside the cell and fuse them with lysosomes to try and kill the pathogens

Question 17

Why is it difficult to intervene with autophagy in the context of toxins?

Answer 17

It is difficult to intervene with toxins because in some ways you may want to stimulate autophagy to try and kill intracellular pathogens but there are pathogens that have evolved to want to be taken up by autophagy so it is very complicated

Question 18

What did Christian de duve win a Nobel prize award for in 1963

Answer 18

Discovering lysosomes
(no knowledge of molecular machinery)

Question 19

What did Oshimi Yoshimori discover in 1992?

Answer 19

Showed autophagy occurred in nitrogen starved and protease deficient yeast

Question 20

How does the autophagy machinery work?

Answer 20

• Lots of bundles of proteins working together including kinases and metabolic pathways
• SNARES

Question 21

How is autophagy selective?

Answer 21

• 4 or 5 proteins have a similar structure where they have a ubiquitin binding domain which is recognised by adaptor proteins which act as a bridge to recruit specific proteins
• A bunch of signalling proteins have their own interacting motif which means they can get sequestered within autophagosomes and get digested

Question 22

What are a lot of disease caused by in terms of autophagy?

Answer 22

• An accumulation of ubiquitinated protein aggregates as a result of a lack of autophagy
• In each neurodegenerative diseases, a different protein is the aggregate and effects a different part of the brain

Question 23

What happens within the Huntington protein that causes Huntington’s disease?

Answer 23

• Polyglutamine expansions within the Huntington’s protein, the longer the tract the more likely you are to get Huntington’s disease
• More than 35 polyQ expansions = disease causing
• PolyQ expansions causes a misfolded protein
• Problems arise if the rate of folding gets higher

Question 24

Why do diseases get worse as you get older?

Answer 24

Capacity for autophagy decreases

Question 25

What happens to the damaged Huntington’s proteins?

Answer 25

• Microaggregates can be degraded
• If there is too much of the misfolded Huntington’s protein, autophagy cannot occur and the proteins will clump together as an attempt to isolate them from the rest of the cell
• Other proteins which interact with the Huntingtons protein will be degraded/isolated too which contributes to neural death

Question 26

What percentage of Parkinson’s cases are familial and what does this imply?

Answer 26

• 5-10% cases are familial
• Not one causative gene rather multiple genes that interact to cause it

Question 27

What mutation prevalent in Parkinson’s disease blocks proteins from being taken away?

Answer 27

• A53T mutation blocks degradation by blocking chaperone mediated autophagy pathway

Question 28

Why are there lots of damaged mitochondria in Parkinson’s patients?

Answer 28

Mutations in two familial genes:
PINK1: Loss of function in mitochondrial kinase
PARKIN: Ubiquitin ligase mutated (damaged mitochondria are not digested)

This leads to oxidative stress and neuronal damage

Question 29

How would autophagy work in being tumour suppressive?

Answer 29

Keeping cells healthy and getting rid of damage

Question 30

Which gene is required in autophagosome formation and how is this relevant in regards to cancer patients?

Answer 30

• Beclin1
• Beclin1 is deleted in 40-75% of breast and ovarian cancers meaning the cell can’t autophage and there is an accumulation of cell damage

Question 31

What is pro-oncogenic autophagy?

Answer 31

• Initially in tumour formation autophagy is tumour suppressive
• However when the tumour starts to grow autophagy helps its survival

Question 32

How is autophagy and apoptosis linked?

Answer 32

• They work together so that you either commit to one pathway: death or survival
  -Bcl2 suppresses release of cytochrome from mitochondria, inhibiting apoptosis
• Beclin and Bcl2 bind and when they do both of their roles are shut off so beclin cannot form autophagosomes and bcl2 cannot inhibit apoptosis
• It also means that if your a cell that activates the pathway you automatically inhibit apoptosis

Question 33

What are the medical implications of this?

Answer 33

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