Autophagy in NDDs

Question 1

Autophagy protects against neurodegeneration by eliminating two hallmarks of NDDs:

Answer 1

– defective mitochondria

– toxic protein aggregates

Question 2

Why are dmaaged mitochondria bad & contribute to NDDs

Answer 2

– produce high levels of reactive oxygen species (ROS)

– pose a threat to cellular components (proteins, lipids and DNA)

Question 3

Why are protein aggregates bad and contribute to NDDs

Answer 3

–exacerbated by ROS- mediated oxidative damage
– compromise the function of organelles
– are particularly toxic for neurons

Question 4

link b/t autophagy and NDDs

Answer 4

Reduced autophagy (age- related, pharmacologically or genetically caused) increases the risk of NDDs

Question 5

These Markers of dysfunctional autophagy are detected in samples from patients with NDDs

Answer 5

– autophagosome accumulation

– limited degradation of p62 (autophagy receptor normally degraded by autophagy)

Question 6

Deletion of Atg5 or Atg7 in the mouse CNS during embryonic development results in

Answer 6

neurodegeneration

KO of these genes causes early degen

Question 7

How can we use autophagy to treat NDDS

Answer 7

By Pharmacologically stimualting autophagy–potential therapeutic strategy against NDDs

Question 8

Autophagy in HD

Answer 8

Disruptions in autophagy are thought to contribute to the pathogenesis of HD
• Catch 22: autophagy is required for clearance of aggregated proteins, but mHTT interrupts the process (i.e. autophagy clears aggregates but mHTT + aggregates interrupt autophagy)

Question 9

Brains of HD patients (and rodent models) contain

Answer 9

contain an excessive number of autophagosomes

Question 10

In HD, autophagy is affected at several steps:

Answer 10

• defect in cargo loading
• trafficking of autophagosomes
• decreased fusion between autophagosomes and lysosomes

Question 11

Alterations in autophagosomes in HD

Answer 11

• The ability of autophagosomes to recognize cytosolic cargos is largely defective in HD cells (autophagosomes appear “empty”)
• mHTT disrupts autophagosome motility and prevents autophagosome
  fusion with lysosomes

Question 12

Aberrant binding of mHtt to p62

Answer 12

• shields p62 binding site

* prevents selective recognition of mitochondria, lipid droplets, and cytosolic aggregates of mHtt

Question 13

Autophagy in AD (

Answer 13

AD brains contain numerous immature

autophagasomes particularly in dystrophic neurites

Question 14

T/F: Autophagy has a clear role in AD

Answer 14

FALSE
• Inconsistent evidence of the role of autophagy:
– evidence of roles in Ab clearance AND role in A-beta production

Question 15

Nature of the autophagic dysfunction in AD

Answer 15

Is unclear (and opposing!!)

• impaired autophagy initiation
• Increased autophagy initiation
• impaired cargo degradation

Question 16

How Ab can regulate autophagy:

Answer 16

– Ab increase autophagy (activation of AMPK)
– Aβ42 compromises the function of AMPK and impedes initiation of autophagy
– Ab decreases autophagosome clearance

Question 17

Autophagy over the disease course

Answer 17

• Initially autophagy may be protective by clearing:
– toxic Aβ species (aggrephagy)
– injured lysosomes (lysophagy)
• BUT in Advanced disease: toxic burden exceeds cellular reparative capacity: neuronal death may follow
May be initially helpful, but pathogenic processes may eventually compromise the
impermeability of endolysosomal compartments

Question 18

Autophagy in PD

Answer 18

• Autophagy is disrupted at multiple stages in PD

- Autophagosomes accumulate when mutant or even WT α-synuclein is overexpressed in transgenic mice

Question 19

Wildtype vs. mutant alpha-synucleuin

Answer 19

• Wt α-synuclein is degraded by CMA
• Mutant α-synucleins are degraded by autophagy
• CMA is compromised in PD –> leads all forms of α-synuclein become degraded by autophagy
  • Autophagosomes accumulate when mutant or even WT α-synuclein is overexpressed in transgenic mice

Question 20

How autophagy leads to excess intracellular levels of α-synuclein

Answer 20

– impairs autophagosome biogenesis by interfering with PAS formation
– decreases lysosomal acidification and slows lysosomal protein turnover

Question 21

PD & lysosomes

Answer 21

Some patients develop PD due to loss-of-function mutations of lysosomal ATPase
– cells with high lysosomal pH
– proteolytic failure

Question 22

Mitophagy

Answer 22

selective degradation of mitochondria by autophagy

Question 23

Mitochondrondrial dysfunction in PD

Answer 23

Mitochondrial dysfunction is a major pathological feature in PD
- Abnormal mitochondria are eliminated through mitophagy

Question 24

Pink and Parkin

Answer 24

Pink and Parkin are essential for mitophagy

But are mutated in familial PD and decrease mitophagy

Question 25

T/F: mitophagy is the cause of sporadic and familial PD

Answer 25

FALSE

•The relevance of decreased mitophagy in sporadic PD is unclear

Question 26

PINK1

Answer 26

• a serine-threonine kinase
• associates + accumulates in outer memb of damaged mitochondria
• PINK1 phosphorylates Ub conjugated to mitochondrial proteins leading to parkin translocation

Question 27

PARKIN

Answer 27

– E3 ubiquitin ligase that normally localizes in the cytosol
– is recruited to and retained on the mitochondria due to higher affinity with phosphorylated Ub
- parkin brings more Ub –> generates long chains of ubiquitin allow recognition by autophagy receptor –> sent to phagophore for degradation

Question 28

PINK1 and parkin work togetehr

Answer 28

• PINK1 associates + accumulates in outer memb of damaged mitochondria then phosphorylates Ub conjugated to mitochondrial proteins leading to parkin translocation
• Parkin brings more Ub –> generates long chains of ubiquitin allow recognition by autophagy receptor –> sent to phagophore for degradation

Question 29

Alterations in PINK1 and Parkin

Answer 29

Mutations in the genes encoding PINK1 and parkin account for the majority of autosomal-recessive cases of PD
– More than 100 loss-of function mutations have been identified in the PARKIN gene

Question 30

Pink and/or parkin mutations impede mitophagy

Answer 30

– damaged mitochondria accumulate
– initiate apoptosis through:
–> the intrinsic pathway
–> ROS–mediated oxidation of membrane lipids and lysosome membrane destabilization