Lecture 17 - Autophagy 1

Question 1

What is (macro)autophagy ?

Answer 1

Involves the degradation and recycling of cellular components. Invovles the formation of specialised double-membrane structures called (autophagosomes, which enclose portions of cytoplasm, organelles, or protein aggregates.

A mechanism to digest intracellular material.

It delivers cytoplasmic waste materials to the lysosome

Question 2

What are the main steps of autophagy?

Answer 2

1. Initiation
2. Nucleation
3. Elongation (Phagophore)
   4.Closure (autophagosome)
   Lysosome
4. Fusion
5. Acidification and maturation
6. Degradation and recycling (Autolysosome)

Question 3

What are the 2 main sets of pathways for intracellular degradation?

Answer 3

1. The Ubiquitin/ proteasome system (UPS)
2. Autophagy

Question 4

How can autophagy be selective ?

Answer 4

There are many different tyoes including :

Mitophagy - degradation of mitochondria
Reticulophagy
Nucleophagy
Lipophagy - degradation of lipid droplets
Xenophagy - degrades microorgansisms

Question 5

Why do cells need degradation/ autophagy?

Answer 5

Recyclying nutrients, damaged protein/organelle removel, cellular remodelling and intracellular pathogen removal

It is an evolutionary conserved survival mechanism

Question 6

What occurs during Ubiquitin system ?

Answer 6

Certain cargo proteins are targeted for degradation by Ubiquitin attachment. Ubs is a small protein. Ubs is recognised by proteasome and fed through and degraded.

Non-lusosomal
Degrades individual proteins
Major turnover route for short-lived proteins

Question 7

What are the 3 compartments of Autophagy ?

Answer 7

Macroautophagy
Chaperone-Mediated Autophagy
Microautophagy

Question 8

What are the features of Macrophagy pathway ?

Answer 8

Lysosomal
Bulk digestion pathway
can remove whole organelles
Molecules released can support metabolism

Question 9

What are the features of chaperone-mediated autophagy/ microautophagy?

Answer 9

Lysosomal
Only degrades individual proteins
Important in aging
Turns over specific, generally long-lived proteins
Relatively low capacity

Question 10

What is useful about Nutirent recycling?

Answer 10

Autophagy is upregulated under starvation.
Causes non-selective bulking

Cells lacking autophagy die under starvation
Autophagy-deficient mice die during neonatal starvation
Cancer calls in solid tumours need autophagy to survive

Question 11

What is useful about cellular remodelling ?

Answer 11

Autophagy is the ONLY mechanism to degrade organelles at once.
Essential to form some specific cell types e.g.
Erythropoiesis - red blood cell differentiation
Removal of sperm-derived mitochondria

Question 12

What is useful about the removal of damaged components ?

Answer 12

Cellular components accumulate damage over time.

Mechanical damage
Damaged mitochondria selectively removed

Ageing and neurodegenerative disease:
Cells continuously acquire damage
Lysosomal capacity decreases as we age
Reduced autophagy is the major reason for age-related degeneration
Long-lived or highly metabolic cells such as neurons and muscles most susceptible. Muscle dystrophy
Cancer

Question 13

Can autophagy make you live longer?

Answer 13

If you restrict calorifc intake you can increase autophagy and therefore increase damage repair - The dietary restriction hypothesis. This increase in damage repair hypothetically stops aging.

Expirements used C.elegans (worms) to test this

Question 14

What is useful about killing intracellular pathogens?

Answer 14

Problem is that Many pathogens escape into the cytoplasm, by being taking up by phagasomes but can prevent maturation of phagosomes. In the cytocol the pathogens are able to easily grow and burst out

Without autophagy = cells more sensitive to infection

Tuberculosis
MRSA
Viruses

Question 15

What are the 4 man roles of autophagy ?

Answer 15

Recycling nutrients
Cellualer remodellin
Intracellu;ar pathogen removel
Damaged proteins

Question 16

How did we discover the pathway ?

Answer 16

Discoverd a mitochondria within a lysosme in 1963. Without knowledge of molecular machinery.

Then in 1992 another man found the same thing in yeast. Instead of many lysosomes yeast have only one central vacuole.

Question 17

WHat did idntifying the Atg genes allow ?

Answer 17

DISRUPTED AUTOPHAGY TO INVESTIGATE ITS FUNCTION

It was a start on dissecting how the machinery works

Observation of autophagy in live cells

Question 18

WHat did idntifying the Atg genes allow ?

Answer 18

ISRUPTED AUTOPHAGY TO INVESTIGATE ITS FUNCTION]

It was a start on dissecting how the machinery works

Observation of autThophagy in live cells

Question 19

Whta re the main proteins and genes involved in autopjagy

Answer 19

1. ULK1 kinase requird for helping start the antire autophay pathwya off
2. PI3K - defines where autophagasomes form
3. 10 gene complex - Controls addition of new lipid to it
4. SNARES regulate fusion of phagasomes with lysosomes

Question 20

How can autophagy be selective aka when the person is starving?

Answer 20

Uses 2 thing

Ubibiquitin tag-cell will be targeted

Adaptor proteins - scaffolding protein with 2 domains. Atg8 (LC3) is a small portion that gets lipide and incorporated into the membrane and Ubiquitin tag.

The adaptor will drag anything ubiquitinated