7. Kane lecture 11/9

target cells of ionizing radiation
thymic lymphocytes, intestinal epithelium (undergo apoptosis)
target cells of hormonal withdrawal
prostatic atrophy, breast epithelial cells (undergo apoptosis)
target cells of toxicants like dioxin
thymic lymphocytes (undergo apoptosis)
target cells of ischemia and reperfusion
cardiac myocytes, neurons (stroke) (undergo apoptosis)
Parkinson’s disease
apoptosis of midbrain dopaminergic neurons; unknown cause
ced genes
regulate apoptosis in humans and C. Elegans (Death)
caspases
Cysteine ASPartate-specific proteASES = homologues of ced genes
procaspases / structure
substrates for active caspases; active caspase then cleaves another procaspase in a catalytic cascade. NH2—–ala-leu-asp—–glut—-
substrates for active caspases (4)
1. procaspases, 2. cytoplasmic DNase (CAD) 3. cytoskeletal proteins 4. nuclear lamins (scaffold of nuclear envelope)
Apaf-1
Apoptotic Protease Activating Factor. binds procaspase 9; this complex is cleaved by cytochrome C; cleavage requires ATP
2 pathways leading to apoptosis and their mechanisms
intrinsic (mitochondrial) – injury or hormone or growth factor withdrawal > active caspase 9. extrinsic (death receptor) – FAS, TNF receptor > active caspase 8
active caspases 8 and 9
activate executioner caspases 3, 6, and 7, which are responsible for the morphlogical aspects of apoptosis
executioner caspases 3>6>7 do what (3)
proteolysis of cytoskeleton and nuclear laminin, transglutaminase cross-linking of proteins, endonuclease activation
Bcl-2 functions
an antiapoptotic factor balanced with Bax, a proapoptotic factor. an increase in Bax relative to Bcl-2 allows release of cytochrome C from the mitochondrion to the cytoplasm where it activates Apaf-1; this activation requires ATP (vs. necrosis which happens because there is no ATP), and it triggers the caspase cascade leading to apoptosis
increased cytosolic calcium, ROS, lipid peroxidation>
mitochondrial injury or dysfunction. membrane is perforated with necrosis but intact with apoptosis (its just that cytochrome c gets released to destroy cell)
apoptosis serves to eliminate severely damaged cells without
eliciting a host response
anticancer treatments act through
apoptosis
irreversible mitochondrial damage= (3)
inability to generate ATP, release of mitochondrial calcium stores, mitochondrial membrane damage
irreversible plasma membrane damage = (3)
structural breakdown, enzymatic breakdown, loss of permeability barrier to calcium
how do you necrose a cell
need both irreversible mitochondrial and plasma membrane damage
t/f final pathways of cell damage are often the same, regardless of the initial cellular targets
true
consequences of injury depend on cell type
heart – necrosis fast. T cells in thymus – apoptosis.
response depends on nature of injury, duration and severity
hormonal withdrawal vs. apoxia
calcium overload
is hypothesized to mediate the structural and functional alterations characteristic of necrotic cell injury.
acute liver damage
jaundice (bilirubin build-up), high serum transaminases (holes in plasma membrane let enzymes out into the blood)
chronic liver damage
jaundice (decreased bilirubin metabolism), decreased serum albumin, clotting factors (decreased protein synthesis)
prototypes and pathogenesis of cell injury (3)
free radical induced injury (stealing electrons from stuff), chemical toxicity (CCl4 – mediated by free radicals, and ethanol), ischemia
biochemical pathways which may generate reactive oxygen species (4)
respiratory chain enzymes of mitochondria – reduction to H20 to make ATP. peroxisomes are membrane-bound organelles in liver that metabolize long-chain FAs to H2O2. NADPH oxidase – activates phagocytes to generate H2)2 or hypochlorous acid. P450 mixed function oxidase – metabolizes drugs/hormones/chemicals in sER in liver
NO that is synthesized from _ by _ can generate _
arginine, nitric oxide synthase, other oxidizing species – important in killing infectious organisms at the expense of damage to adjacent host tissue
sources of free radicals (3)
hyperoxia, ionizing radiation, reperfusion following ischemia (oxidants released from phagocytic cells in the restored circulation)
catalase
defense mechanism in peroxisomes
Mn-superoxide dismutase
defense mechanism in the mitochondria
Cu-Zn SOD
defense mechanism in cytosol
which vitamins have antioxidant properties / what are the properties
A, C, E, beta-carotene / effective against damage to lipids by OH* = third layer of defense against free radicals (antioxidants)
3 tiers of antioxidant defense mechanisms
1. SOD converts superoxide anion to H2O2. 2. catalase converts H2O2 to water and oxygen. 3. metal chelators
superoxide-driven Fenton reaction
= iron-catalyzed Haber-Weiss reaction. O2-* + H2O2 > OH* = really bad because OH* is very reactive. reaction is catalyzed by free iron or copper
superoxide anion
O2-*
normally iron/copper is tightly bound to (3)/(1)
ferritin, transferrin, or hemoglobin / ceruloplasmin
GSH
=glutathione. glutathione peroxidase reduces GSH into GSSG while turning hydrogen peroxide into 2water
glutathione reductase
converts GSSG back to GSH
depletion of cellular GSH can result from 4 mechanisms:
decreased synthesis because of fasting or AA deficiency (cysteine, serine, glycine, and homocysteine – requires ATP); generation of high levels of oxidants/toxic metabolites leads to accumulation of GSSG and its transport out of the cell; redox cycling of chemicals such as the herbicide paraquat = oxidative stress; metabolism of exogenous chemicals by p450 may produce intermediates that covalently bind to SH groups in proteins – these thiols then react with GSSG (or the intermediates react directly with GSH and deplete its stores)
what causes protein breakdown and DNA damage (specifically)
increased intracellular calcium and ROS
what happens when oxidants attack proteins? (3)
cross-linking at suflhydryl groups, decreased enzyme activity (especially ATP-dependent ion umps), abnormal protein folding or aggregation
what happens to misfolded proteins
they’re degraded by the proteasome complex
hsp
heat shock proteins are induced in cells under stress (infections, oxidant stress, high temp) = chaperones for proper folding
ubiquitin
a hsp that binds to damaged proteins and targets them to the proteasome complex for degradation
accumulation of excess misfolded proteins does what? where do they accumulate?
can trigger apoptosis / in ER
ER stress
unfolded protein response
alzheimer disease
disease induced by chronic accumulation of misfolded proteins in the ER of cells (ubiquitin isn’t doing its job)