Unit I: Apoptosis Flashcards
Necrosis- 4 major differences from apoptosis
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- 4.
Necrosis
- Cell dissolution with extrusion of contents
- acute inflammatory response
- tissue architecture is lost, cellular loss is obvious because lots of cells die at once
- cell swells and blebs before dying
Apoptosis- 4 main different features
- cell fragments, but contents do not get out
- no inflammation
- tissue changes aren’t apparent (one cell dies at a time)–architecture preserved
- condensation of cell, break up of cell
apoptotic bodies
cell fragments due to apoptosis. No extrusion of intracellular contents. remember cell SHRINKS before fragmenting.
Mechanisms of apoptosis (x5)
- loss of growth factor/stimulation
- Fas-Fas killing of infected cells
- P53 killing of damaged cells
- mis-folded protein accumulation
- maintenance of cell populations (embryogenesis, epithelial layers, immune)
Apoptotic cells microscopic features
EOSINOPHILIC
- cell shrinks (condensation of nucleus and cell)
- chromatin is at periphery of nucleus under nuclear membrane
- membrane blebbing
Why isn’t cell loss apparent in __(apoptosis or necrosis)___ ?
(x3)
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Apoptosis- cell loss is not apparent due to:
- cells die singly or in small clusters
- space is filled in by movement of surrounding cells
- no inflammation
In viral hepatitis, cells undergo
BOTH apoptosis and necrosis
What happens to cell fragments in
- Apoptosis
- Necrosis
- Apoptosis- cell fragments are phagocytosed by surrounding cells (magrophages and parynchyma)
- Necrosis- phagocytosed by macrophages, initiate acute inflammatory response?
Caspase
- what is it?
- activation?
- cysteine proteases that cleave aspartic acid= Caspase
- zymogens that require activation by initators or autolytic activation.
Caspases- function/effect (x2 major ones)
- cleave nuclear and cytoskeletal scaffold (LAMINS)==> protein cross-linking and cytosolic condensation
- triggers endonuclease activity
Endonucleases
- activation?
- function?
- mechanism?
- activated by caspases, require Mg or Ca
- DNA breakdown
- Calcium and Mg dependent endonucleases break down DNA into 50-300kB pairs==> 180-200 bp. Internucleosomal DNA cleavage.
How are apoptotic cells phagocytosed (mechanism)? X2 “markers”
- Phosphatidyl serine on plasma membrane is flipped and faces outwards, marking a cell as an apoptotic body.
- external expression of thrombospondin
Phagocytosed by MACROPHAGES= minimal inflammation
Physiological vs Pathological processes of apoptosis
Initiation of apoptosis: Major pathways
- Bcl Pathway
- Fas-Fas pathway
Bcl-2 proteins
- Sensors- what are they, how are they activated, what is their function?
- Effectors- what are they, function, regulation?
- Regulators - what are they, function, regulation?
- Bcl-2 family of proteins in mitochondria- pro and anti-apoptotic members
- cytoplasmic signaling influences balance of pro/anti
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Sensors: BH3
- Activated by decreased survival signals, DNA damage, ER stress (protein misfolding)
- activate Bax/Bak==>form pore
- inhibit Bcl-xl, Bcl-2
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Effectors: pro-apoptotic= Bax/Bak- form pore
- activated by BH3 proteins
- inhibited by Bcl-xl, Bcl-2
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Regulators: anti-apoptotic: Bcl-xl, Bcl-2- inhibit Bax/Bak and other pro-apoptotic proteins
- increased by growth factors and other survival signals
- inhibited by BH3 (= sensors)
Apoptosis Figure
(shows intrinsic and extrinsic pathways)
What happens after Bax/Bak are activated?
- Bax/Bak= pore formed in mitochondria==> cytochrome C leaks out of outer membrane
- Cytochrome C binds Apaf-1 and activates caspase 9
Follicular lymphomas- oncogene?
have an oncogene that activates bcl-2==> inhibition of apoptosis in neoplastic cells
Death receptor pathway- what is it?
2 initiators
Extrinsic pathway of apoptosis
- Fas (CD95) binds FasL (virally infected t-cells)
- TNF/TNF-R crosslinking
Fas-Fas ligand
- mechanism
- purpose
- viral adaptation
- activation of FADD (FAS associated death domain)==> pro caspase 8 activation ==> autolytic activation of other caspases
- killing of autoreactive t-cells
- FLIP (made by viruses) blocks activation of caspase 8
How doe live cells protect themselves from phagocytosis? (how are they differentiated from apoptotic bodies?)
Cd31 expression
TNF family of receptors
- includes TNFR1 and Fas
- Activate FADD or TRADD==> caspase activation
Spinal muscle atrophy- what’s the mutaiton?
mutation in regulatory proteins that inhibit activation of TNF induced apoptosis.
CTL-induced cell death- 2 ways
- CTL’s express FasL and can activate extrinsic pathway via Fas receptor ligation
- CTL recognizes foreign antigen==> expression of perforins create transmembrane pores==>exocytosis of granzyme B (cleave proteins at aspartate residues) ==> activated cellular caspases
- no death receptor activation, no mitochondrial engagement– direct activation of effector phase= caspases.
Decrease in growth factor
Intrinsic pathway-neurons and hormonal signaling
decreased Bcl-2, increased BH3 sensors (bim)
ER stress- what causes it? mechanism? disease examples?
from accumulation of misfolded proteins
- misfolded proteins are ubiquitinized and destroyed by proteosome, but too many overwhelm the process
- ER stress response activates caspases==> apoptosis (intrinsic)
- degenerative CNS disease= alzheimers, parkinsons, maybe DMII
DNA damage apoptosis
- what causes DNA damage
- Cell response?
- Disease example
- heat, radiation, chemo,
- p53 accumulates in cell==> arrest cell cycle at G1==> [if the damge can’t be repaired] trigger apoptosis via sensors (activate Bax/Bak; inhibit Bcl-xl/2)
- p53 mutations allow damaged cells to divide= carcinogenesis
Disease with inhibited apoptosis (x2)
Diseases with increased apoptosis (x3)
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Inhibited apoptosis
- p53 mutation
- autoimmune disorder (cant remove autoreactive t-cells)
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Increased apoptosis
- CNS degenerative disease
- ischemic injury
- virus induced lymphocyte depletion
Autophagy
- autophagic vacuole formed from ribosome free regions of ER digest cell components
- activated by multi-protein units that sens nutrient deprivation
- involved in clearance of misfolded proteins in neurons and hepatocytes
- may trigger apoptosis
