Cell death and damage Flashcards
What is the function of necrosis?
-Removes damaged cells from an organism
Failure to do so may lead to chronic inflammation, more damage subsequently done
- Necrosis causes its own acute inflammation to clear cell debris via phagocytosis
What are the causes of necrosis?
Usually lack of blood supply e.g
Injury
Infection e.g gangrene
Cancer
Infarction
Inflammation
What are the steps of necrosis?
6 steps, start: injurious agent/event.
End” cell membrane ruptured
- Result of an injurious agent or event (whole groups of cells are affected).
- Initial events are reversible, later ones are not. So if conditions are right the cell can undo the damage and survive, only to a certain point before the events are irreversible.
- Lack of oxygen prevents ATP production from glycolysis or TCA cycle
- Cells swell due to the influx of water (ATP is required for ion pump to work). This changes the osmolarity of cytoplasm and puts more pressure on membranes within cell due to expanded volume
- Lysosomes rupture; enzymes degrade other organelles and nuclear material hapzardly random manner
- Cell membrane ruptured, cell debris released in extracellular environment, triggering inflammation
What nuclear changes occur during necrosis?
- Chromatin condensation/shrinkage at beginning of necrosis
- Fragmentation of nucleus, can see chromosomal DNA
- Dissolution of the chromatin by DNAse
What cytoplasmic changes occur during necrosis?
- Opacification: protein denaturation and aggregation to become whiter and more solid mass
- Complete digestion of cells by enzymes causing cell to liquify (liquefactive necrosis)
What biochemical changes occur during necrosis?
- Release of enzymes such as creatine kinase or lactate dehydrogenase
- Release of other proteins such as myoglobin into blood stream and urine
These biochemical changes are useful in the clinic to measure the extent of tissue damage
What is the function of apoptosis? And what is it involved in?
Selective process for the deletion of superfluous, infected or transformed cells
Involved in:
- Embryogenesis
- Metamorphosis
- Normal tissue turnover to be replaced by newer cells
- Endocrine-dependent tissue atrophy
- A variety in pathological conditions
What is the step by step process of apoptosis
- Programmed cell death of one or a few cells – distinction from necrosis which is multiple cells at once, apoptosis is selective
- 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 cytoplasmic changes occur during apoptosis?
- Shrinkage of cell. Organelles packaged into membrane vesicles
- Cell fragmentation. Membrane bound vesicles bud off
- Phagocytosis of cell fragments by macrophages and adjacent cells
- No leakage of cytosolic components – leakage into extracellular environment minimised compared to necrosis where it leaks and triggers inflammation
What nuclear changes occur during apoptosis?
- Nuclear chromatin condenses on nuclear membrane
- DNA cleavage
What biochemical changes occur in apoptosis?
- Expression of charged sugar molecules on outer surface of cell membranes (recognised by macrophages to enhance phagocytosis)
- Protein cleavage by proteases, caspases
What are the two types of apoptosis?
Intrinsic
- DNA damage – p53 dependent pathway
- Interruption of the cell cycle
- Inhibition of protein synthesis
- Viral infection ie once virus is in the cell
- Change in redox state
Extrinsic – relative to the cell not body
- Withdrawal of survival factors e.g mitogens
- Extracellular signals e.g TNF
- T cell or NK (natural killer) e.g Granzyme
What are caspases?
Involved in apoptosis.
The point of convergence for causes of apoptosis. Extrinsic and intrinsic causes feed into casases, causing apoptosis.
Caspases are cytesine proteases (cysteine aspartate-specific proteases) - cysteine is the type of protease caspase is, aspartate is the amino acid motif
Describe activation of caspase
Inactive procaspase is cleaved by upsteam caspase in two places, releasing n terminal prodomain. Turns inactive procaspase into active caspase.
Describe the caspase cascade
Top caspase in cascade is initiator caspase – in humans this is typically 8 and 9
Activates downstream caspases which typically activates many more further downstream
Not just activation of caspases, downstream caspases have additional substrates that are not caspases. Get cleavage of cytosolic proteins and nuclear lamin proteins (nuclear envelope proteins)
Caspases with additional substrates are effector caspases (in humans 1,3,6,7) more and more molecules with each step
Not a linear cascade but like a pyramid
There is signal amplification
In ligand induced multimerisation, what do the death adaptor and receptor share?
What do the death adaptor and procaspase-8 share?
What domain does procaspase-8 contain?
What do shared domains between proteins allow?
- The death domain
- Death effector domain
- Death effector doman and protease domain, catalytic part.
- Allow proteins to bind together because similar domains will dimerise/multimerise.
Explain ligand induced multimerisation in Tumour necrosis factor (TNF)
- TNF bound to ligand binding domain of TNFR, bringing death domains into close proximity
- Creates environment where dimerisation with other proteins with death domains is favoured
- Death adaptor protein, FADD creates environment with high conc. of death effector domain proteins
- Death effector proteins recruit procaspases-8. Multi-protein complex has assempled - called DISC, death-inducing signaling complex
- Catalytic domains of procaspase-8 in close proximity, activate themselves
- Get proteolysis, caspases become active.
- Caspase-8 production from procaspase-8
- Caspase-8 departs from membrane into cytoplasm, activates caspase cascade
Cytochrome C-induced apoptosis
What domain is shared between APAF-1 (apoptotic protease activating factor 1) and procaspase-9?
What domain is on procaspase-9?
Where is the cytochrome c binding site?
- Caspase recruitment domain (CARD)
- Protease domain.
- On APAF-1.
