Cell Death Flashcards
Why does type of cell death matter?
- different triggers for each
- different consequences for the cell/ tissue after death for disease progression/ medicines
- necrosis vs apoptosis
apoptosis 5 general characteristics ( swell? compaction? initation? passive/active? inflammatory?)
1) cell shrinks; DNA fragments in 200bp ladder
2) compaction of chromatin; apoptotic body forms
3) imitated by signal transduction
4) active process; requires macromolecule synthesis
5) DOES NOT cause inflammation (can be anti-inflammatory)
is a PROCESS like cell cycle
Necrosis 5 key characteristics? (swell? compaction? initation? passive/active? inflammatory?)
1) cell swelling & DNA fragments random (smear on gel)
2) no chromatin compaction or apoptotic body formation
3) initiated by direct cell damage
4) passive process= no macromolecule synthesis
5) cause inflammation
why does DNA have 200bp ladder in apoptosis?
-because it is the distance between the 2 histones
why does swelling happen in necrosis?
-is passive has no energy & maintaining correct cell plumbness requires energy
nomenclature committee on Cell Death (NCDD)?
1) address related to nomenclature of cell death based on morphological grounds
2) define major cell death on functional basis
3) distinguish essential (causal) vs accessory (correlative) aspects of death process
4) ID consensus criteria for identification of dead cells w/ permeable PM or complete cell fragmentation
two types of apoptosis?
1) intrinsic pathway
2) extrinsic pathway
both w/ specific cascade, both lead to apoptotic bodies w/ membrane blabbing
-both have executioner & initiator caspases
apoptosis
- programmed cell death
- orderly cell self destruction
- this process is as crucial for survival of multi-cellular organisms as cell division
sequence of apoptosis? (x7)
1) enzymes break down cell cytoplasm
2) cytoplasm becomes dense (shrinks)
3) organelles tightly packed
4) cell surface membrane changes, bleb forms
5) chromatin condenses, nuclear envelope breaks
6) cell breaks into vesicles
7) phagocytosis
cell fragments of apoptosis?
- are produced with intact Plasma membrane containing organelles
- are ingested/digested by phagocytic cells
cell fragments of necrosis?
- DO NOT produce blebs w/ intact memrbane
- shit is just falling apart, external parts of cell are now outside it (key part!)
what eats apoptosis vesicles?
- WBC (phagocytes)
- see the plasma membrane and no internal cell parts so calmly disposes of the vesicles
- necrosis WBC in panic because see internal cell organs floating around
what causes apoptosis?
1) normal physiological processes
- healthy & helps us adapt to cell damage we may have
2) pathological processes
Physiological processes that require apoptosis? (x)
1) embryo/fetal development
2) hormone dependent involution
3) cell loss in proliferating cell populations
4) elimination of self-reactive lymphocytes
5) death of cells that have served their function
What is hormone dependent involution?
-ex: regression/ stopping of lactation of breast after weening
Apoptosis & death of cells that have served their function ?
-lymphocytes are hugely activated (in response to pathogen) but no way to deactivate them except to do apoptosis
Apoptosis & elimination of self-reactive lymphocytes ?
- in B & T cells, test to see if they are potentially self reative, if ARE we do apoptoiss.
- If apotptosis doesn’t work then we are at risk for autoimmune disease
Apoptosis in embryo/fetal development?
- frequently make temporary structure in fetal development to get cells from one place to next
- start w/ webbed hands
- incorrect/failure leads to morpholigcal birth defects
pathological reasons for apoptosis? (4)
1) DNA damage due to radiation/chemo
2) accumulation of misfolded proteins–>ER stress–> apoptosis
3) host immune response to virally infected cells
4) organ atrophy after duct obstruction
Viral infections & apoptosis?
- viruses don’t want apoptosis, want cells to stay alive & divide so our host cells are virus factories
- we defend ourselves by killing cells, turning off pathogen factories
caspases?
- apoptosis entirely dependent on their presence
- look for actviated caspapses to see if tissue in apotptosis or necrosis
- mutations cause inability to do apoptosis
- are in PRO-FORM
Apoptosis step 1
activation of initiator caspases by cleavage of pro-caspase
Caspase initation?
- caspases exist in pro-form, must be activated to begin apoptosis by cleavage of the pro-caspase
- pro-caspase portion of caspase have no function other than prevent caspase dimerization and activation
Apoptosis step 2?
- initiator caspases activate executioner caspases
- AMPLIFICATION STEP
- 1 active caspase activates a TON of executioner caspases
-need this because a lot of work has to be done to prepare cell for apoptosis
apoptosis step 3?
- executioner caspases cleave cell proteins, condense & pack chromosomes and cytoplasm, cleave nuclear lamina
extrinsic pathway of apoptosis? (x6)
1) cells have Fas death receptor on surface
2) killer lymphocyte w/ death signal binds Fas receptor
3) pro-caspase binds Fas receptor (both inactive)
4) Killer lymphocyte w/ Fas ligand binds, forms DISC complex
5) DISC activate caspases 8 or 10 via pro form cleavage
6) initiator caspases activate executioner caspases–> apoptosis
expression of fas death receptor on cell membrane?
DOES NOT cause apoptosis, just means is capable of listening to external death signal
do all cells express fas death receptor?
- some always do; some only express in distress,
- one way cells differnetiate between being prone/not prone to apoptosis
- MOST CASES have Fas receptor; NO fas ligand
- only when fas ligand binds receptor, does disc complex get made
intrinsic apoptosis pathway?
1) stressful event occurs, mito disfunctions & releases Cytochrome C into cytoplasm
2) Cytochrome C binds molecules, forms APOPTOSOME
3) apoptosome recruits caspases, forms INFLAMASOME
4) inflamasome activates initiator caspase 9,
5) caspase 9 activates executioner caspases–> apoptosis
Are all molecules that form inflamasome always in the cell?
- depends on how prone cell is to apotptosis, some cells the molecules have to be induced (slow apoptosis requrie txn/trans to make moelcules; like neurons) others will always be present (fast apoptosis like lympphocytes)
- earlier molecules typically trend/trans and ready to go, later molecules haven’t yet
GSK?
- ex of molecule that has different regulatory consequences on the intrinsic & extrinsic pathways
- can cause excessive cell death (neurodegenerative disease; or deficient apoptosis (cancer)
is the SAME GSK-3 either way
Intrinsic pathway and GSK-3?
- GSK-3 exerts a PRO-APOPTOTIC role, acting on targets Bax, Bim, VDAC
- helps in disintegration of mito. & release of cytochrome c
Extrinsic pathway and GSK-3?
- anti-apoptotic, GSK-3 prevents DISC complex formation
- means that initiator caspases can’t be activated, so executioner caspases aren’t formed so no apoptosis
BCL2, BH2, BH123?
BCL2= anti-apoototic ( all 4 domains) BH123 = ppro-apoptoic (3 domains) BH3-only= pro- apoptotic (1 domain)
How BCL2 effect apoptosis? BH3 effect apoptosis?
- is anti-apoptotic, inhibits BH123 protein activation of intrinsic apoptosis pathway
- BH=pro-apoptotic; inactivates BCL2 therefore allows BH123 to dimerize & activate intrinsic apoptosis pathway
how do extracellular survival factors inhibit apoptosis?
1) by inducing expression of Bcl2
2) turning off expression of BH3-only proteins
- which results in increased amounts of activated Bcl2
