ILA 13 Apoptosis Flashcards
What is apoptosis?
The death of cells which occurs as a normal and controlled part of an organism’s growth or development
Slide 4
Why is apoptosis important?
- Cellular Homeostasis - Immune response; water and salt balance; nerve activity; potassium levels; blood pH; tissue development, repair/organ integrity
- Protection - cells harboring dangerous mutations; viral/bacterial infection
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The average adult loses how many cells per day via apoptosis?
50-70 billion
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What are the 3 main modes of programmed cell death distinguished by their morphological changes?
- Necrosis
- Autophagic cell death
- Apoptosis
Apoptosis was initially called “programmed cell death”
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Describe what happens during necrosis.
- enlargement of cell volume
- swelling of organelles
- membrane bursting
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Describe what happens during autophagic cell death.
- “cell death w/ autophagy”; autophagy does NOT induce death; inhibitors for autophagy do not inhibit cell death
- occurs when apoptosis is blocked
- massive vacuolization of cytoplasm which accumulate into autophagosomes
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What are the morphological features of apoptosis?
- cell rounding
- reduction of cellular & nuclear volume
- Pyknosis - chromatin condensation
- Nuclear & DNA fragmentation
- Plasma blebbing
- apoptotic bodies
- engulfment by phagocytes
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Explain what it seen in the picture.
What is responsible for this pattern?
DNA Laddering
Caspase activated- DNAse cuts DNA 200 base pairs
*only see this pattern on gel with apoptosis
caused by nuclear fragmentation of the apoptotic cell
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What is blebbing?
- results when the cell’s cytoskeleton breaks up causing the membrane to bulge
- Bulges may break from the membrane forming apoptotic bodies. These bodies are taken up by phagocytes.
Slide 10
How does phosphatidylserine (PS) recognition work?
how does it cause apoptosis?
Normal Cells–> PS is on cytosolic side of plasma membrane
Apoptotic cells–> PS gets flipped to the extracellular side of the plasma membrane where it is recognized by receptors on phagocytes and engulfed
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What is used to distinguish between the three types of PCD?
Morphological changes induced in each cell defines the pathway of death induced
Question directly from powerpoint
Slide 35
What are the key morphological changes brought on by apoptosis? (These are used for diagnosis)
Pyknosis, nuclear and DNA fragmentation, plasma blebbing
Question directly from the powerpoint
Slide 35
What are the 2 main pathways of apoptosis?
Intrinsic & Extrinsic
Main difference b/w 2 is Initiation. Execution & Phagocytosis are same
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How does initiation occur in the intrinsic pathway?
also called mitochondrial pathway
initiated by signals from the cell’s own genes or detection of intracellular proteins that recognize DNA damage and involve the inhibition of anti- and activation of pro-apoptotic BCL2-proteins
includes genotoxic stress & growth factor removal
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How does genotoxic stress induce apoptosis??
- Double stranded breaks activate PI3 kinases such as ATM and DNA-PKcs
- results in activation of p-53 which in turns activates the BCL-2 protein BAX
Slide 15
How does growth factor (GFs) removal induce apoptosis?
Removal of GFs which signal cell proliferation can cause apoptosis through activation of BAX
(ex. IL-2 stimulate T cell proliferation during immune response or Vascular Endothelial Growth Factor (VEGF) which promotes angiogenesis)
Slide 15
What is occurring in B cell lymphoma-2 (BCL-2)?
- translocation mutation carried by pts w/ follicular variant of b-cell lymphoma
- results in BCL2 overexpression
- BCL-2 does NOT promote cell proliferation; it inhibits apoptosis of cancerous B cells
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What are the antiapoptotic regulators?
Bcl-2 and Bcl-xL
bind pro-apoptotic proteins (BAX/BAK) keeping them inactive
What are the multidomain proapoptotic regulators?
- Bax and Bak
- These proteins are bound in their inactive form by BCL-2 in the cytoplasm
What are the BH3-only proapoptotic regulators?
- Bid, Bad, Noxa, Puma, Bim
- These proteins bind BCL-2 releasing it from BAX/BAK
Why is active BAX or BAK dangerous?
- Once in its active form, BAX or BAK migrates to the mitochondria where it forms a pore within the outer mitochondrial membrane
- This releases Cytochrome C stored in the intermembrane space –> APOPTOSIS
What makes up the DISC (Death-inducing signal complex)?
FADD & Pro-caspase 8
What are the two ligands for death receptors?
FasL and TNF-α
Formation of the DISC causes what?
activation of pro-caspase 8 which in turn activates caspase 3 leading to Apoptosis
