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7/29/2019 Apoptosis Usjb8im
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APOPTOSIS: An overview
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INTRODUCTION
Cell death by injury
-Mechanical damage
-Exposure to toxic chemicals
Cell death by suicide
-Internal signals-External signals
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Conted…..
Apoptosis or programmed cell death, is carefullycoordinated collapse of cell, protein degradation ,
DNA fragmentation followed by rapid engulfment
of corpses by neighbouring cells. (Tommi, 2002)
Essential part of life for every multicellular
organism from worms to humans. (Faddy et al.,1992)
Apoptosis plays a major role from embryonic
development to senescence.
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Why should a cell commit suicide?
Apoptosis is needed for proper development
Examples:
– The resorption of the tadpole tail
– The formation of the fingers and toes of the fetus
– The sloughing off of the inner lining of the uterus
– The formation of the proper connections between neurons in the brain
Apoptosis is needed to destroy cells
Examples:
– Cells infected with viruses
– Cells of the immune system
– Cells with DNA damage
– Cancer cells
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What makes a cell decide to commit suicide?
Withdrawal of positive signalsexamples :
– growth factors for neurons
– Interleukin-2 (IL-2)
Receipt of negative signals
examples :
– increased levels of oxidants within the cell
– damage to DNA by oxidants
– death activators :
• Tumor necrosis factor alpha (TNF-)
• Lymphotoxin (TNF-β)
• Fas ligand (FasL)
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Necrosis vs. Apoptosis
• Cellular condensation
• Membranes remain intact
• Requires ATP
• Cell is phagocytosed, no
tissue reaction
• Ladder-like DNA
fragmentation
• In vivo, individual cells
appear affected
• Cellular swelling
• Membranes are broken
• ATP is depleted
• Cell lyses, eliciting an
inflammatory reaction
• DNA fragmentation is
random, or smeared
• In vivo, whole areas of
the tissue are affected
Necrosis Apoptosis
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NECROSIS Vs APOPTOSIS
Wilde, 1999
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STAGES OF APOPTOSIS
Sherman et al., 1997
Induction of apoptosis related genes, signal transduction
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membraneblebbing &changes
mitochondrialleakage
organelle
reduction
cell
shrinkage
nuclear
fragmentation
chromatin
condensation
APOPTOSIS: Morphology
Hacker., 2000
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membrane blebbing & changes
mitochondrial leakage
organelle reduction
cell shrinkage
nuclear fragmentation
chromatin condensation
APOPTOSIS: Morphological events
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Bleb
Blebbing & Apoptotic bodies
The control retained over the cellmembrane & cytoskeleton allows intact
pieces of the cell to separate forrecognition & phagocytosis by M s
Apoptotic body
M M
C
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Caenorhabditis elegans
1090 cells 131 cells apoptosis
ced-1ced-2ced-5ced-6ced-7ced-10
ced-3ced-4
ced-9 egl-1
ces-1 ces-2
nuc-1
execution decisionto die
engulfment degradation
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Apoptosis: Pathways
Death
Ligands
Effector
Caspase 3
Death
Receptors
Initiator
Caspase 8
PCD
DNAdamage
& p53
Mitochondria/
Cytochrome C
Initiator
Caspase 9
“Extrinsic Pathway”
“Intrinsic Pathway”
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MAJOR PLAYERS INAPOPTOSIS
• Caspases
• Adaptor proteins• TNF & TNFR family
• Bcl-2 family
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Ligand-induced cell death
Ligand Receptor
FasL Fas (CD95)
TNF TNF-RTRAIL DR4 (Trail-R)
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Ligand-induced cell death
“The death receptors”
Ligand-induced trimerization
Death Domains
Death EffectorsInduced proximity
of Caspase 8
Activation of
Caspase 8
FasL
Trail
TNF
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p53
Apoptosis events
Initiator caspases 6, 8 , 9,12
Activators ofinitiator enzymes
Apoptotic signals
Execution caspases 2, 3, 7
APOPTOSIS: Signaling & Control pathways I
Externally driven
Internally
driven
Cytochrome C
Externally driven
Activation
mitochondrion
O OS S S C
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p53
ExternalInternal
Apoptosis events
Initiator caspases 6, 8 , 9,12
Activators ofinitiator enzymes
Apoptotic signals
Execution caspases 2, 3, 7 Inhibitors of
apoptosis
APOPTOSIS: Signaling & Control pathways II
Inhibitors
Externally driven
Internally
driven
Cytochrome C
Externally driven
Survivalfactors
Bcl2
Inhibition
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H2O2
Growth factor
receptors
casp9Bcl2
PI3K Akt
BAD
Apaf1
Cyt.C ATP
The mitochondrial pathway
casp3
casp3
IAPs
Smac/DIABLO
AIF
Bax
Bax
p53
Fas
Casp8
Bid
Bid
Bid
DNA
damage
Pollack etal ., 2001
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REGULATION OF APOPTOSIS
Stimuli apoptosis selection of targets (Rich et al., 2000)
Apoptosis by conflicting signals that scramble thenormal status of cell (Canlon & Raff, 1999)
Apoptotic stimuli cytokines, death factors (FasL)
(Tabibzadeh et al., 1999)
DNA breaks p53 is activated arrest cell cycle oractivate self destruction (Blaint & Vousden, 2001)
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Importance of Apoptosis
• Important in normal physiology / development – Development: Immune systems maturation,
Morphogenesis, Neural development
– Adult: Immune privilege, DNA Damage and wound
repair.
• Excess apoptosis – Neurodegenerative diseases
• Deficient apoptosis – Cancer
– Autoimmunity
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FUTURE PERSPECTIVES
The biological roles of newly identified death
receptors and ligands need to be studied
Need to know whether defects in these ligandsand receptors contribute to disease
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CONCLUSION
an important process of cell death
can be initiated extrinsically through death ligands(e.g. TRAIL, FasL) activating initiator caspase 8 throughinduced proximity.
can be initiated intrinsically through DNA damage (viacytochrome c) activating initiator caspase 9 througholigomerization .
Initiator caspases 8 and 9 cleave and activateeffector caspase 3, which leads to cell death.
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DNA DAMAGE
p53
The bcl 2 family
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The bcl-2 family
BH4 BH3 BH1 BH2 TM N C
Receptor domain
phosphorylation
Raf-1calcineurin Pore
formation
Membraneanchor
Liganddomain
Group I
Group II
Group III
Bcl-2
bax
Badbid bik
Back
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P53 & Apoptosis
p53 first arrests cell growth between G1 S
This allows for DNA repair during delay
If the damage is too extensive then p53
induces gene activation leading to
apoptosis (programmed cell death)
BACK
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3 mechanisms of caspase activationa. Proteolytic cleavage e.g.
pro-caspase 3
b. Induced proximity, e.g.
pro-caspase 8
c. Oligomerization, e.g. cyt c,
Apaf-1 & caspase 9
Back
A t i i l t kill i f t d ll
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Cytolytic lymphocyte/CTL (& natural killer lymphocyte)
presents Fas ligand/CD178 on its surface to tell the infected
cell to die
Apoptosis events
Initiator caspases
Apoptotic signals
Execution caspases
Externally driven
Cytochrome c
Fas ligand
Apoptosis signal to kill infected cells
Fas/ CD95 is the
The immunological synapse holds the cellsmuch tighter togetherthan shown here
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