Cell Injury (Drake) Flashcards
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Apoptosis
Programmed cell death (physiological or pathological)
Single cells
Requires ATP
No loss of membrane integrity
Little release of cell contents (apart from extrusion-planned)
Little inflammation
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Causes of Necrosis
(1) ischemia
(2) mitochondrial poisoning
(3) membrane damage agents (ROS, bacterial enzymes)
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Sequence of events for cell death in ischemia
1) Decreased blood flow
2) Decreased oxygen
3) Decreased ATP
4) Decreased Na/K pump (increased cytoplasmic Na+ and Ca++)
5) Loss of mitochondrial electron transport function
6) Loss of inner mitochondrial membrane integrity
7) Lysosomes degrade cell constituents
PROCESS IS REVERSIBLE UNTIL LOSS OF INNER MITOCHONDRIAL MEMBRANE INTEGRITY
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Consequences of ischemia
Decreased oxidative phosphorylation –> decreased ATP –>
(1) ER swelling Cell swelling (decreased Na+ pump activity)
(2) clumping of nuclear chromatin
(3) decreased protein synthesis and increased lipid deposition
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Role of increased cytosolic Calcium in cell injury
activation of cellular enzymes–>
(1) membrane damage (due to phospholipases and proteases)
(2) nuclear damage (due to endonucleases)
(3) decreased ATP (due to ATPase activity)
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Clinical conditions leading to necrosis
Ischemia and hypoxia
Ischemia reperfusion injury
Inflammation and infections
Chemical injury
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Stages of apoptosis
- Signaling stage - Initiation (generate activated initiator caspase from procaspases)
- Effector stage - Death pathway engaged (caspase cascade generates effector caspases)
- Terminal stage - Cell death. Morphologic changes. (endonucleases digest DNA, cytoskeleton broken apart)
- Phagocytosis of apoptotic cell
Necrosis
Occurs in many adjacent cells
Passive response
Does not require ATP
Disruption of organalle fxn
Release of cell contents
Strong inflammatory rxn
Always pathological
What are all initiators of necrosis associated with?
Decreased ATP
How can you tell if a tissue is undergoing necrosis?
Released intracellular proteins enter the blood and are measured as markers of tissue damage (eg liver enzymes; cardiac enzymes and proteins).
Where does the intrinsic pathway of apoptosis occur?
Mitochondria
Molecules involved in intrinsic pathway of apoptosis
1) Bcl2 (regulator): sits on membrane of mitochondria and binds Bax/Bac to keep it from forming mitochondrial pores; is anti-apoptotic
2) Bax/Bac (effector): forms pore in mitochondrial outer membrane; is pro-apoptotic
3) BH3 (sensor): when cell wants to undergo apoptosis, BH3 binds to Bcl2, freeing Bax/Bac to form mitochondrial pores; is pro-apoptotic
After mitochondrial pore is formed in intrinisc pathway of apoptosis, what happens?
Cytochrome C and other proteins released into cytoplasm –> initiates formation of caspase complex called apoptosome –> caspase pathway that leads to apoptosis
Extrinsic pathway of apoptosis
Fas death receptor present on all cells binds Fas ligand on killer T cell –> aggregate –> adaptor protein FADD attracts procaspase (forming DISC complex) –> initiate effector caspase cascade –> apoptosis
Terminal stage of apoptosis
Executioner caspases: activate endonucleases (DNA fragmentation), degrade microfilaments (cytoplasmic blebbing), proteolyse lamin (nuclear blebbing)
Transglutaminase inside cell does protein cross-linking
Why doesn’t apoptosis result in inflammation?
No release of cytokines
Apoptotic cells are rapidly cleared
Plasma membrane is preserved
Apoptotic cells secrete inhibitors of inflammation
Diseases that result from apoptosis (both decreased and increased apoptosis)?
Decreased: cancer, viral infection (herpes), autoimmune (lupus)
Increased: Alzheimers, Type I diabetes, organ atrophy, ischemia (myocardial infarction, stroke)
Reactive Oxygen Species (ROS)
Molecules that can generate free radicals and/or are already free radicals
How are cells exposed to ROS?
1) Normal oxidative phosphorylation
2) Activation of certain receptors
3) Chemicals from environment
4) Metabolites of drugs and environmental agents
5) Impaired function of defense enzymes/mechanisms
ROS negative effects on proteins
1) Modification of SH groups (S-S crosslinking)
2) Adduct formation with lysine, tyrosine, cysteine
3) Protein unfolding
4) Protein scission (splitting apart)
ROS negative effects on lipids
1) Changes in membrane fluidity (damage membrane)
2) Production of receptor ligands
3) Become antigenic
4) Lipid ROS propagates ROS formation (BAD! Due to double bonds of fatty acids)
5) Fatty acid oxidation
6) Scission of lipids (measure malondialdehyde to see if this is happening)
7) Cross-linking lipids
ROS negative effects on DNA
1) Base mutations/changes (usually by adding hydroxyl radical; some lead to apoptosis)
2) Chromosome breaks
Glutathione (GSH)
Very important antioxidant (a metabolite)
Turns H2O2 –> H2O (in general quenches oxygen free radicals)
HIGH ratio of reduced to oxidized glutathione (GSH:GSSG) tells you that there’s no cellular oxidative stress
Glutathione peroxidase
Enzyme that catalyzes the reaction of Glutathione with H2O2 to turn it into H2O (also at the same time turns GSH to GSSG)
Glutathione reductase
Enzyme that catalyzes the reaction where GSSG reduces NADPH to NADP+ (at the same time turns GSSG to GSH)
Fixing lipid free radicals: Vitamin E (tocopherol) and Vitamin C (ascorbic acid)
Antioxidants (metabolites)
Vitamin E in plasma membrane finds lipid free radicals and gets rid of them but turns into a free radical itself!
Vitamin C in water soluble compartment picks up radical from vitamin E
Other enzymes get rid of Vitamin C’s free radical
Enzymes to get superoxide to H2O
Superoxide dismutase (SOD): superoxide (O2) –> H2O2
Catalase: H2O2 –> H2O
Heme oxygenase
Controls free iron in the process of heme catabolism
(Fe2+ can generate hydroxyl radical!)
Fixing protein free radicals that create damaged or unfolded proteins
1) Chapreone synthesis: they help re-fold proteins
2) Ubiquitin: tag misfolded proteins and degrade
3) Unfolded protein response (UPR): turn on tx of genes to respond to ROS stress (glutathione, folding proteins, etc) and turn off translation of unnecessary proteins
Fixing DNA free radicals that cause DNA damage
Just repair DNA as usual!
Ends in inhibition of cell cycle or apoptosis if damage is severe
How do cells detect ROS via Nrf2?
Nrf2 is a TF that binds antioxidant response element (ARE) and increases expression of things to get rid of ROS (GSH, proteasome, anti-inflammatory)
Normally, Nrf2 constantly made and degraded
Nrf2 is normally bound to Keap1 (sensory molecule) which promotes degradation by ubiquitin
ROS prevents Keap1 from binding Nrf2 (ROS oxidizes thiols on Keap1) so Nrf2 increases
How do cells detect hypoxia via HIF?
HIFa and HIFb complex is TF that initiates tx of genes to restore O2, energy homeostasis, OR initiate apoptosis
Normally, HIF constantly made and degraded
HIFa normally has PHD (sensory protein) add OH, which promotes degradation by ubiquitin
ROS inactivates PHD so it can no longer tag HIFa with OH for degradation, so HIF increases
