apoptosis. normal development e.g. immune system when does apoptosis occur?
TRANSCRIPT
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APOPTOSIS
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APOPTOSIS
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Normal development e.g. immune system
WHEN DOES APOPTOSIS OCCUR?
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Disease states e.g. Alzheimer’s disease
WHEN DOES APOPTOSIS OCCUR?
Amyloid plaques in the brain
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NECROSIS APOPTOSIS
TYPES OF CELL DEATH
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MorphologicalNECROSIS
• loss of membrane integrity
• swelling of cytoplasm & mitochondria
• total cell lysis• no vesicle
formation• disintegration of
organelles
APOPTOSIS • Membrane blebbing, no loss of
integrity• Aggregation of chromatin at
nuclear membrane• Shrinking of cytoplasm &
nuclear condensation• Fragmentation into smaller
bodies• Formation of apoptotic bodies• Mitochondria become leaky
TYPES OF CELL DEATH
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Biochemical
NECROSIS• Loss of regulation of
ion homeostasis• No energy
requirement• Random digestion
of DNA• Postlytic DNA
fragmentaion• Tightly regulated
process
APOPTOSIS • Energy dependent• Non random DNA
fragmentation• Prelytic DNA fragmentation• Activation of caspase cascade• Release of various factors into
cytoplasm
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physiologicalNECROSIS
• Affects groups of cells
• Evoked by non physiological disturbances
• Phagocytosis by adjacent cells
• Significant inflammatory response
APOPTOSIS • Affects individual cells• Induced by physiological
stimuli• Phagocytosis by macrophages • No inflammatory response
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Caspases – key executioners of apoptosis
(cysteinyl aspartate specific proteases)
Highly conserved proteases14 homolgues inactive zymogens
Caspases divided into
1) Initiator caspases: Caspases 2, 8,9,10 or
2) Effector caspases: caspase 3,6,
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Properties of proteases
Irreversible -
Autocatalytic: triggered by cofactor
binding or inhibitor removal
Proteases can regulate their own
activation
Have protease, will have inhibitor
specificity
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Caspase structure
3 domains 1) highly variable
NH2 domain2) large subunit (~20kD)3) small subunit
( ~10kD)
Highly specific absolute requirement for cleavage after aspartic acid
recognition of at least 4 amino acids NH2 terminals to the cleavage site
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Caspase structure
2 key features: variable N domain regulates activation
all domains derived from proenzyme at cleavage specific sites
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Basic apoptotic machinery
DNA fragmentation,
chromatin condensation,
membrane blebbing,
cell shrinkage &
disassembly into apoptotic bodies
engulfment. 30-60 min
effectors responsible for cellular changes associated with apoptosis. Caspases inactivate proteins that protect cells from apoptosis
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How do caspases disassemble a cell? It slices, it dices
Selective cleavage of specific proteins
eg bcl-2, or CAD/ICAD
e.g. nuclear lamina
eg. Gelsolin
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What triggers apoptosis?
• Loss of contact with surroundings
• Irreparable internal damage
• Conflicting signals for cell division
• Specific ‘death ligands’
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How are caspases activated?
More than one way to skin a cat
activation of downstream, effector caspases
Proteolytic cleavage
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How are caspases activated?
More than one way to skin a cat
Induced proximity
aggregation of multiple procaspase-8 molecules into close proximity somehow results in cross-activation
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How are caspases activated?
More than one way to skin a cat
Holoenzyme formation
Activation of caspase-9 is mediated by means of conformational change, not proteolysis
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The roads to ruin
The nematode C.elegans
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The roads to ruin Mammals
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External signalsdriven by death receptors (DR) e.g. CD95 (or Fas/Apo)
Each CD95L trimer binds to 3 CD95 leading to DD clustering.
FADD ( Fas associated death domain/ Mort 1) binds via its own DD
Caspase –8 oligomerisation drives activation through self cleavage
Caspase –8 then activates downstream effector caspases like caspase –9 (CED-9 homolog)
Apoptosis initiation
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Internal signals
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BCL-2
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apoptosis
DNA damage
Death
receptors
Growth
factor
withdrawal
TRIGGER
P53
Bcl-2 family
Death domain
factor
Cytochrome c
oncogenes
REGULATOR
Apaf-1
Caspases
EXECUTIONER