L3: Cell death & cell damage Flashcards
What are the functions of necrosis?
→Removes damaged cells from an organism
→causes acute inflammation to clear cell debris via phagocytosis
What does lack of necrosis lead to?
→may lead to chronic inflammation
What are some examples of causes of necrosis?
Usually lack of blood supply, e.g. →injury, →infection, →cancer, →infarction, →inflammation
What can be observed in necrosing tissues as distance from blood vessels increases?
→ as distance increases
→pH and pO2 reduces
Describe the necrosis process
→Lack of oxygen prevents ATP production → increased osmolarity.
→Cells swell due to influx of water (ATP is required for ion pumps to work).
→Lysosomes rupture; enzymes degrade other organelles and nuclear material hapzardly
→Cellular debris released, triggering inflammation
What is a difference between the early and later stages of necrosis?
→first stage is reversible mitochondrial changes unlike apoptosis
What are the microscopic changes that occur during necrosis?
- Chromatin condensation/shrinkage.
- Fragmentation of nucleus.
- Dissolution of the chromatin by DNAse.
What are the cytoplasmic changes during necrosis?
- Opacification: protein denaturation & aggregation.
2. Complete digestion of cells by enzymes causing cell to liquify (liquefactive necrosis).
What are the biochemical change that during necrosis?
- Release of enzymes such as creatine kinase or lactate dehydrogenase
- Release of other proteins such as myoglobin
Why are biochemical changes useful for?
→to measure the extent of tissue damage
What is the function of apoptosis?
Selective process for the deletion of superfluous, infected or transformed cells.
What is apoptosis involved in?
→Embryogenesis
→Metamorphosis
→Normal tissue turnover
→Endocrine-dependent tissue atrophy
Describe the apoptosis process
→Events are irreversible and energy (ATP) dependent.
→Cells shrink as the cytoskeleton is disassembled.
→Orderly packaging of organelles and nuclear fragments into membrane bound vesicles.
→New molecules are expressed on vesicle membranes that stimulate phagocytosis without an inflammatory response.
What are the differences between apoptosis and necrosis?
→apoptosis involves cell death of one of a few cells, necrosis is a group of cells
→ apoptosis is irreversible, necrosis’ early stage is reversible
→ no leakage of cytosolic components
What are the cytoplasmic changes during apoptosis?
- Shrinkage of cell. Organelles packaged into membrane vesicles.
- Cell fragmentation. Membrane bound vesicles bud off.
- Phagocytosis of cell fragments by macrophage and adjacent cell.
- No leakage of cytosolic components
What are the morphological features of apoptosis?
→Cytoplasm shrinks around nucleus
→Vesicles bud from cell (“blebbing”)
What are the nuclear change during apoptosis?
- Nuclear chromatin condenses on nuclear membrane.
2. DNA cleavage.
What are the biochemical changes apoptosis?
→Expression of charged sugar molecules on outer surface of cell membranes
→Protein cleavage by proteases, caspases
Why are charged sugar molecules expressed during apoptosis?
→recognised by macrophages to enhance phagocytosis
What does DNA fragmentation show of necrosis and apoptosis?
apoptosis= bands down the gel necrosis= DNA smear, non-specific digestion
Give examples of apoptosis?
→Cell death in embryonic hand to form individual fingers.
→Apoptosis induced by growth factor deprivation (neuronal death from lack of NGF).
→If DNA is damaged due to radiation or chemo therapeutic agents, p53 (tumour suppressor gene product) accumulates.
→Cell death in viral diseases (ie viral hepatitis
→Death of neutrophils during an acute inflammatory response
When does p53 trigger apoptosis?
→If DNA is damaged due to radiation or chemo therapeutic agents, p53 (tumour suppressor gene product) accumulates.
→This arrests the cell cycle enabling the cell to repair the damage.
→If repair process fails, p53 triggers apoptosis.
Give an example of a viral disease which causes apoptosis
→viral hepatitis
What are the two types of apoptosis?
→intrinsic
→extrinsic
What is involved in intrinsic apoptosis?
→DNA damage – p53-dependent pathway →Interruption of the cell cycle →Inhibition of protein synthesis →Viral Infection →Change in redox state
What is involved in extrinsic apoptosis?
→Withdrawal of survival factors e.g. mitogens
→Extracellular signals (e.g. TNF)
→T cell or NK (Natural Killer) (e.g. Granzyme).
What do extrinsic and intrinsic apoptosis have in common?
→caspases
What are caspases?
→cysteine aspartate-specific proteases
→form an activation cascade, where one cleaves and activates the next
What are caspases analogous to?
→kinase cascades
Give examples of initiator caspases
→8,9
Give examples of effector caspases
→1, 3, 6, 7
What shape does the caspase cascade form?
→pyramidal
→signal amplification
Where are lamin proteins found?
→found in nuclear membrane
Give examples of caspase targets and their function
→Lamin A and B=Nuclear envelope →PARP= DNA repair →DNA-PK= DNA repair →Toposiomerase II = DNA replication →Raf-1= Signalling →Akt/PKB= Cell survival →STAT1= Signalling →eIF4= Translation
What does caspase activation lead to?
→shrinkage, chromatin condensation,
→DNA fragmentation
→plasma membrane blebbing
How are initiator caspases activated?
→activate themselves when in close proximity to each other
How is extrinsic apoptosis induced?
→by ligand binding to receptors, causing receptor dimer- (or multimer-) isation
What allows proteins bind together?
→shared domains
What are the three death domains in ligand-induced multimerization?
→death domain
→death effector domain
→protease domain(catalytic)
What is FADD?
→FAS-Associated protein with Death Domain
What is DISC?
→Death-inducing signalling complex
What is intrinsic apoptosis induced by?
cytochrome c released from mitochondria
What is an exception to intrinsic apoptosis?
→growth factor withdrawal (extrinsic apoptosis) an exception that uses cytochrome c
What is cytochrome C?
→Mitochondrial matrix protein
→released in response to oxidative stress by a “permeability transition”
What are the players in cytochrome C-induced apoptosis?
→cytochrome C
→cytochrome c binding site
→APAF domain
→Caspase recruitment domain (CARD)
What is APAF-1?
→Apoptotic ProteaseActivating Factor
What is procaspase-9 involved in?
→intrinsic apoptosis
How is the release of cytochrome c from the mitochondria regulated?
→a pore made of BLC-2 family proteins
What does BCL-2 do?
→form pore through which cytochrome C leave
What can BCL-2 proteins be?
→pro or anti apoptosis
Give examples of anti-apoptotic BCL-2 proteins
→bcl-2, bcl-XL
→Repress cytochrome c release
Give examples of pro-apoptotic proteins
→Bax, Bad, Bid
→Facilitate cytochrome c release
What do BCL-2 proteins have in common?
→BH3 domain used to form dimers
What does BAD do to BCL-2 protein?
→BAD binds strongly to BCL2 so it doesn’t bind to pore
→ cytochrome c Is released
If BCL-2 family proteins regulate cytochrome C release from mitochondria, what regulates BCL-2 proteins?
→TP53
→TP53 increases BAX transcription
→new pores inserted into membrane
→cytochrome leaves
Give an example of growth factors with BAD
→survival signals →Akt/PKB phosphorylates of BAD
→BADd doesn’t bind to BCL-2
→BCL-2 is free to bind to pore and cytochrome doesn’t leave cell
