Chapter 2: Cell Responses to Stress and Toxic Insults: Adaptation, Injury, Death Flashcards
Pathology
study of structural, biochemical, functional changes in cells, tissues, organs that underlie disease
Disease
any deviation/interruption of the normal structure of a part, organ, system of the body as manifested by characteristic symptoms and signs
Disorder
a derangement or abnormality of function; a morbid physical or mental state
Neoplasm
any new and abnormal growth, specifically new growth of tissue in which the growth is uncontrolled and progressive
4 aspects of the disease process
- etiology- cause; genetic or acquired
- pathogenesis- biochemical and molecular mechanisms of disease
- morphologic changes: structural alterations induced in cells and organs; used to follow disease progression
- clinical manifestations: functional consequences of the changes
Adaptations
reversible functional and structural responses to change in physiologic states/pathologic stimuli, during which new but altered steady states are achieved, allowing the cell to survive and continue to function
Hypertrophy
adaptation involving increase in cell size
Hyperplasia
adaptation involving increase in cell number
Atrophy
adaptation involving decrease in cell size, number, and metabolic activity
Decreased nutrients, decreased stimulation
Metaplasia
adaptation involving change in phenotype of cells
due to chronic irritation
Syndrome
A set of symptoms that occur together; a symptom complex; the sum of signs of any morbid state
Cell injury
due to reduced O2 supply, chemical injury, microbial infection
Cellular aging
cumulative sublethal injury over long life span
Transitioning myocardial cells show what?
adaptation–>cell injury–>cell death
Triphenyltetrazolium colors myocardium magenta to see this
adapted: hypertrophy due to increased BP because of the mechanical effort needed
reversibly injured: no gross/microscopic changes, but cellular swelling and fat accumulation
What is the most common stimulus for skeletal muscle hypertrophy?
increased work load
What is the most common stimulus for hypertrophy in cardiac muscle?
increased hemodynamic load from HTN or faulty valves
Cardiac hypertrophy causes release of what?
TGF-beta, IGF1, FGF, vasoactive factors (alpha-adrenergic agonists, endothelin 1, and angiotensin II)
What pathways are activated when cardiac hypertrophy occurs?
PI3K/AKT (important in exercise hypertrophy) and G proteins (important in pathologic hypertrophy)
Next step after the activation of the 2 pathways
TF’s are activated (GATA4, NFAT, and MEF2) which work to increase the synthesis of more proteins–>hypertrophy
What happens when the genes for the heart are switched back to the fetal form?
myosin heavy chain reverts to the B form instead of the A isoform–>slower contraction, conserves energy
Cardiac hypertrophy also causes increased ANP release…why?
usually only seen in embryological heart
ANP is increased because it causes Na+ secretion from the kidney–>decreases blood volume and pressure–>reduces hemodynamic load
Eventual conclusion of heart hypertrophy
myocardial fibers undergo lysis and loss of contractile elements–>myocyte death can occur
To prevent this, inhibitors of NFAT, GATA4, and MEF2 are given
Hormonal hyperplasia
female breast (glandular epithelial cells) during puberty or pregnancy
Compensatory hyperplasia
occurs when a lobe of a liver is donated and the remaineder of the liver grows back to compensate for the loss
intrahepatic stem cells regenerate during hepatitis
Bone marrow after blood loss/hemolysis
What causes pathologic hyperplasia?
excessive amounts or inappropriate actions of hromones/ GFs acting on target cells
Endometrial hyperplasia
the balance between estrogen and progesterone is disturbed and the relative or absolute amount of estrogen is increased that causes hyperplasia of the endometrial glands
leads to abnormal menstrual bleeding
at risk for developing endometrial cancer
What causes benign prostatic hyperplasia
increased stimulation by androgens
Can viruses cause hyperplasia?
Yes
When is cell death seen during atrophy?
Not in the beginning
seen in tissues where there is loss of endocrine or factors or blood supply
Physiological atrophy
notochord
thryoglossal duct
uterus after parturition
Causes of pathological atrophy
decreased workload (atrophy of disuse): initially reversible, but if prolonged–>apoptosis
Loss of innervation (denervation atrophy)
Diminished blood supply: ischemia–>atrophy
Inadequate nutrition
Loss of endocrine stimulation
Pressure
Senile atrophy
atherosclerosis of blood vessles leading to the brain or heart–>atrophy of brain/heart
Inadequate nutrition leading to atrophy
profound protein-calorie malnutrition (marasmus)
results in cachexia that is often from pts with cancer and chronic inflammatory diseases
What causes wasting of the muscle tissue in cancer?
TNF: suppresses appetitie and lipid depletion
Loss of endocrine stimulation causing atrophy
loss of hormones to hormone sensitive tissues like the breat, uterus, and vagina–>atrophy
Pressure causing atrophy
tissue compression
can compress surrounding uninvolved tissues
Tumor pressing on the rest of the brain causes atrophy due to a loss of blood supply to the affected area
Mechanisms of atrophy
decreased protein synthesis and increased protein degradation
synthesis decreases due to a lowered metabolic activity
How does degradation of cellular proteins mainly occur?
ubiquitin pathway
caused by nutrition deficiency and disuse
mostly seen in cachexia
What is atrophy commonly associated with?
increased autophagy
marked by increased amounts of autophagic vacuoles
Autophagy
when starved cells eats its own components in attempt to reduce nutrient damage to match the supply
Lipofuscin
indigestible that remains as a membrane bound residual body
give tissue a brown appearance–>brown atrophy
Metaplasia
a REVERSIBLE change in which one differentiated cell type is replaced by another
What is the point of metaplasia?
New cell type can cope better to stress than the original one
Vitamin A deficiency
epithelium changes from columnar to stratified squamous
Adenocarcinomas
glandular cancer
can come from long-term Barrett’s esophagus
Connective tissue metaplasia
The creation of cartilage, bone, or adipose tissue in tissues that do not normally contain these elements
Myositis ossificans
occurs after intramuscular hemorrhage in which there is bone creation inside the muscle
seen as an adaptive response to cell tissue/injury
Mechanism of metaplasia
the phenotype of the already differentiated stem cell does not change, instead it is the reprogramming of what the stem cell produces
What is metaplasia the result of?
stimulation from cytokines, growth factors, and ECM signals–>drive cells toward a specific differentiation pathway
How does Vit A deficiency cause metaplasia?
it is a transcription factor that needs to bind to the nuclear retinoid receptor to influence the differentiation of tissues
Reversible cell injury
occurs in the early stages or mild forms of cell injury
reversible if damage stimulus is removed
Examples of reversible cell injury
reduced oxidative phosphorylation and lower ATP
cell swelling from water influx
organelles may show alterations
Cell death
continuing damage until cell cannot recover and the cell dies
the point of no return is different for all cells: heart and CNS are very sensitive
2 types of cell death
necrosis
apoptosis
Necrosis
due to loss of cell membranes and loss of ion homeostasis
always pathologic
lead to inflammation
Apoptosis
when DNA is damaged beyond repair
pathologic or physiologic
nuclear dissolution, fragmentation of cell (without the loss of membrane integrity), rapid removal of cell debria
NO INFLAMMATION because contents do not leak
Causes of cell injury
O2 deprivation chemical agents and drugs physical agents infectious agents immunological reactions genetic derangements nutritional imbalances-excess and deficiencies
First thing that happens in cell injury
at the molecular/biochemical level and then progress to be able to be seen at the structural level
gross morphology changes before cell death
Reversible morphological changes in cell injury
cell swelling
blebbing of cell membrane
detachment of ribosomes from ER
clumping of nuclear chromatin
Hydropic change
aka vacuolar degeneration
small clear vacuoles seen in the cytoplasm under the microscope from pieces of the ER that have been pinched off and released
Fatty changes
reversible injury
occurs in hypoxic, toxic, and metabolic injury
manifested by appearance of lipid vacuoles in cytoplasm
seen in cells dependent on fat metabolism-hepatocytes, myocardial cells
Plasma membrane alterations in reversible injury
blebbing, blunting, and loss of microvilli
Mitochondrial changes in reversible injury
swelling and the appearance of small amorphous densities
Dilation of the ER in reversible injury
detachment of polysomes, intracytoplasmic myelin figures may be present
nuclear alterations in reversible injury
disaggregation of granular and fibrillar elements
Necrosis
result of denaturation of the cell’s proteins and enzymatic digestion of the lethally injured cell
Why does necrosis lead to inflammation?
Contents leak out of leaky membranes due to lysosomes of the dying cell and lysosomes of the leukocytes involved in the inflammation
When can necrosis be noticed?
Takes a few hours to see histologically, but can see markers in the blood within a coupld of hours due to loss of plasma membrane integrity
Morphology of necrosis
shows increased eosinophilia due to loss of RNA and denatured proteins
Glassy appearance- loss of glycogen
cytoplasm appears vacuolated and moth-eaten when the organelles are digested
Myelin figures
replace dead cells
large, whorled phospholipid masses that come from damaged cell membranes
eventually eaten by other cells and broken down into fatty acidsy, which can be calcified into calcium soaps
What does necrosis show under EM?
discontinuities in the plasma and organelle membranes
dilation of mitochondria with large amorphous densities
intracytoplasmic myelin figures
debris
aggregates of fluffy material (denatured proteins)
Karyolysis
basophilia of chromatin can fade from the loss of DNA due to endonucleases
nuclear fading
chromatin dissolution due to action of DNAses and RNAses
Pyknosis
nuclear shrinkage and increased basophilia from the chromatin condensing into a solid basophilic mass
also seen in apoptosis
nuclear shrinkage
Karyorrhexis
pyknotic nucleus fragments and then within a day or two the cell disappears
nuclear fragmentation
Coagulative necrosis
almost always related to blood flow abnormality
tissue has a firm texture
eosinophilic anucleate cells
proteins denature with the enzymes that would have cleaned them up, so they remain around for awhile
What causes coagulative necrosis?
obstruction of a blood vessel that leads to necrosis
Infarct
localized area of coagulative necrosis
Liquefactive necrosis
characterized by digestion of the dead cells that turns the dead tissue into a liquid viscous mass
Brain tissue
What tissue cannot undergo coagulative necrosis?
Brain
What causes liquefactive necrosis?
bacterial or fungal infections since they stimulate lots of leukocytes to come to the area and digest everything
Appearance of liquefactive necrosis
creamy yellow because of dead leukocytes–>pus
Hypoxic death of CNS cells cause what kind of necrosis?
Liquefactive
What tissue does liquefactive necrosis normally occur in?
Brain
Gangrenous necrosis
not a specific pattern, but a common term used in clinical practice
What part of the body normally gets gangrenous necrosis?
lower limbs
Wet gangrene
bacterial infection superimposed on it and there is some liquefactive necrosis present also
Caseous necrosis
often from TB infections
Cottage cheese-like (white)
Intracelllar accumulation
Accumulation of abnormal amounts of harmless/harmful substances in cytoplasm, organelles, nucleus
4 main pathways of intracellular accumulation
Inadequate removal of a normal substance due to defects in packaging and transport—>fatty changes (steatosis) in the liver
Accumulation of an abnormal endogenous substance as a result of genetic or acquired defects in folding, packaging, transport, or secretion—>mutated forms of alpha1- antitrypsin
Failure to degrade a metabolite due to inherited enzyme deficiencies—>results in storage diseases, progressive and fatal to tissue and pts
Deposition and accumulation of abnormal exogenous substances when the cell is not able to digest or move it—>accumulation of Carbon or silica particles
Why do lipids accumulate intracellularly?
From an abnormal metabolism
What lipids accumulate intracellularly?
TAGs, cholesterol, phospholipids
Phospholipids in myelin figures
Occurs in lysosomal storage disease
Steatosis
Fatty change
Abnormal accumulation of TAGs within parenchymal cells
Often seen in the liver since it does a lot with fat metabolism but also occurs in the heart, kidney, and muscle tissue
What causes steatosis?
Toxins, protein malnutrition, DM, obesity, anoxia
Steatosis histologically
The well preserved nyc is squeezed into the displaced rim of cytoplasm about the fat vacuole
Cholesterol and cholesterol esters
Cells use cholesterol for membrane synthesis, but not accumulation
Atherosclerosis
Smooth muscle cells and macrophages within the intima layer of IgA’s fill with lipid vacuoles containing cholesterol and cholesterol esters—>foam cells
Foam cells
IgA’s that have their cells in the intima layer filled with lipid vacuoles containing cholesterol and cholesterol esters
Appear yellow and foamy
May rupture—>lipids into extracellular space—>crystallize
Xanthomas
Clusters of foam cells (often macrophages) that accumulate in the subepitheliela CT of the skin and in tendons that form tumors
Cholesterolosis
Accumulation of foam cell macrophages in the lamina propria of the gallbladder
Neumann-Pick disease type C
Lysosomal storage disease that affects an enzyme that moves cholesterol around
Results in cholesterol accumulation in lots of organs
Why do proteins accumulate intracellularly?
Defect in protein folding/transport
Morphology of protein accumulation
Intracellular accumulation appear as rounded, eosinophilic droplets, vacuoles, or aggregates in the cytoplasm
By EM, they are amorphous, fibrillar, or crystalline
Causes of protein accumulation
Reabsorption droplets in proximal renal tubules
Russell bodies
Defective intracellular transport and secretion of critical proteins
Accumulation of cytoskeleton proteins
Aggregation of abnormal proteins
Reabsorption droplets in proximal renal tubules
Seen in renal diseases that have proteinuria
If the glomerulus lets many proteins into the filtrate, it reabsorbed via Pinocchio’s is in PT into vesicles—>protein appears as pink hyaline droplets within the cytoplasm of PT cells
Reversible if the proteinuria diminishes and the droplets are allowed to be metabolized
Russell Bodies
In cells that are producing lots of cells very quickly, like in synthesis of Igs in plasma cells, the ER becomes very distended and produces large, homogenous eosinophilic inclusions
Defective intracellular transport and secretion of critical proteins
In alpha1-antitrypsin deficiency, mutations in the protein—>slow folding—>building of partially folded intermediates in cell and not secreted
The pathology comes from both the lack of the protein (that causes emphysema) and from apoptosis due to ER stress
Accumulation of cytoskeletal proteins
Accumulation of keratin filaments and neurofilaments are associated with cell injury
Alcoholic hyaline
In Alzheimer’s, the neurofibromas tangle found in the brain contains neurofilaments and other proteins
Alcoholic hyaline
An eosinophilic cytoplasmic inclusion in liver cells that is commonly seen in alcoholic liver disease
Accumulation of keratin intermediate filaments in the cells
Aggregation of abnormal proteins
Abnormal or misfolded proteins may deposit intracellularly, extracellularly, or both
Cause direct or indirect effects
Certain forms of amyloidosis fall into this category
Called proteinopathies or protein-aggregation diseases
Hyaline change
A change that occurs within or outside of cells that makes it look homogenous, glassy, and pink when stained with H/E
Describes a variety of alterations, not a specific pathway of cell injury
Russel bodies, alcoholic hyaline, reabsorption droplets
Extracellular hyaline change
Occurs in DM and chronic HTN
Walls of the arterioles (esp. in the kidney) become hyalinized due to extravasated plasma protein and deposition of basement membrane material
Glycogen intracellular accumulation
Seen in pts with glucose or glycogen metabolism defects, collectively called glycogen storage diseases or glycogenosis
Appear as clear vacuoles within the cytoplasm
Appears best in tissues fixed in absolute alcohol
Staining with best carmine or the PAS reaction makes it look more rose/violet
Glycogen accumulation and DM
Glycogen is found in the renal tubular epithelial cells, liver, Beta cels of islets of Langerhans, and heart muscle cells
Exogenous pigments
Most common is carbon from pollution in urban areas
Breathed in, picked up by macrophages and taken to regional lymph n odes in the tracheobronchial region
Blackens the lungs (anthracosis) and involved LNs
Can also be caused from carbon dust most often seen in CoA miners—>causes fibroblastic emphysema that is now as coal workers pneumoconiosis
Tattooing
Pigments enter the skin and are phagocytized by dermal macrophages where they live for the rest of the individual’s life
Endogenous pigments
Lipofuscin
Melanin
Homogentisic acid
Hemosiderin granules
Lipofuscin
Lips broke or wear and tear pigment
Insoluble pigment
Composed of polymers of lipids and phospholipids complexed with protein
Comes from lipid peroxidation of polyunsaturated lipids of subcellular membranes
Not inherently dangerous to cells, but useful in finding cells with ROS damage
How does lipofuscin appear?
As a yellow-brown, finely granular cytoplasmic and perinuclear pigment
What cells is lipofuscin found?
Cells undergoing slow/regressive changes and is found most often in the liver and heart of aging pts, severe malnutrition, and cancer cachexia
What is the pigment of aging?
Lipofuscin
Cells undergone repeated damage
Melanin
Brown-black pigment formed by tyrosinase during the oxidation of tyrosine to dihydroxyphenylalanine in melanocytes
Only one of this color
Homogentisic acid
Black pigment that occurs in pts with allkaptonuria that is deposited in the skin, CT, and cartilage
Pigmentation by this condition is called ochronosis
Hemosiderin granules
Hb derived Yelllow/brown; crystalline or granular Major storage form of iron Formed by aggregates of ferritin micelles (hemosiderin + apoferritin) when there is an excess of iron Easily seen on light microscope
What cells have hemosiderin granules?
Normally in cells that are engaged in breaking down old RBCs in the spleen, liver, and bone marrow
Local overload causes there to be hemosiderin in cells, which local overload causes it to be in the tissues
Bruises are an example of what type of pigment?
Hemosiderin granules
Once the RBCs are let out into the tissue, macrophages come and break down the hgb to recover the iron
The heme is converted to biliverdin (green) then to bilirubin (red)
Hemodiderosis
Systemic overload leads to deposition of hemosiderin in organs
Mostly caused by hemochromatosis, hemolytic anemia, and repeated blood transfusions
Pathologic calcification
Abnormal tissue deposition of Ca (mostly), Fe, and Mg
Can be either dystrophic or metastatic
Dystrophic
Occurring locally in dying tissues
Metastatic
Deposition in normal tissues
Usually secondary to a disturbance in Ca2+ metabolism
Asbestosis
Ca and Fe gather along the long asbestos shards and created beaded dumbbell forms
Morphology of calcification
Appear microscopically as a white granular clump
In time, heterotropic bone may be formed in the focus of calcification
Single necrotic cells may have seed crystals that become encrusted in mineral deposits
Psammoma bodies
Progressive acquisition of outer lamellated configs
Some types of cancer, like thyroid
What can a tuberculous lymph node be converted to?
A stone
What is the appearance of Ca on H/E?
Basophilic
Is calcification intracellular or extracellular?
Both
Dystrophic calcification
Found in areas of necrosis, damaged, or aging tissue
Almost always found in the atheromas of advanced atherosclerosis
Commonly happens in aging or damaged heart valves
Wear and tear—>Ca deposits on leaflets—>not pliable over time
Ductal carcinoma in situ
Grows at such a rate that outgrows blood supply
Dystrophic calcification
What is the level of serum calcium in dystrophic calcification?
Normal
Metastatic calcification
May occur in normal tissues whenever there is hypercalcemia
Causes of hypercalcemia—>metastatic calcification
Increased levels of PTH from hyperparathyroidism leading to increased bone reabsorption
Bone tumors leading to reabsorption of bone
Vit D disorders
Renal failure
Alcohol intoxication
Milk-alkali syndrome
Examples of bone tumors leading to the reabsorption of bone
Multiple myeloma Leukemia Breast Pagets disorder (accelerated bone turnover) Immobilization
Vitamin D disorders—>metastatic calcification
Vitamin D intoxication
Sarcoidosis (macrophages activate a vitamin D precursor)
Idiopathic hypercalcemia of infancy (Williams syndrome)
Renal failure—>metastatic calcification
Leads to retention of phosphate and secondary hyperparathyroidism
Milk-alkali syndrome
Excessive ingestion milk and antacids
Granuloma
area composed of a collection of fragmented and lysed cells and amorphous granular debris within a distinctive infalmmatory border
Granulomatous inflammation
collection of macrophages, often with T cells, sometimes associated with central necrosis
Fat necrosis
not a specific pattern, but a common term used in clinical practice
released enzymes split the triglyceride esters in fat cells which combine with Ca2+ to produce a chalky-white appearance
Pancreatitis and fat necrosis
local areas of fat destruction from pancreatic lipases that were released into the peritoneal cavity
Fat saponification
When FAs combine with Ca2+ and have a chalky-white appearance
Fat necrosis histologically
see foci of shadowy outlines of necrotic fat cells with basophilic Ca2+ deposits surrounded by an inflammatory reaction
Fibrinoid necrosis
special form that involves blood vessels
typically happens when complexes of Ags and Abs are deposited in the walls of arteries
these deposits can then leak out of the vessels and result in a bright pink and amorphous appearance in H/E stains that are called fibrinoid
Dystrophic calcification
if necrotic cells are not taken back up by leukocytes, they can become a nidus for Ca2+ and other salts and become calcified
Cell Injury depends on…
the nature, duration, and severity of the injury
Consequences of cell injury depend on
type, state, and adaptability of the injured cell
includes nutritional/hromonal status, metabolic needs, vulnerability, ability to rest, polymorphisms in genes
What does cell injury result from?
biochemical mechanisms acting on several essential cell components
What are the cell components damaged most frequently during cell injury?
mitochondria, cell membranes, machinery of protein synthesis and packaging, DNA
What happens when ATP is depleted 5-10%?
Na+/K+ ATPase pump is reduced
cell energy metabolism is altered
Ca2+ pump failure
Consequences of reduced Na+/K+ pump
Na+ retention in cells–>H2O goes into cells–>cell swelling–>cell lysis
Consequences of cell energy metabolism alteration
Loss of ATP–>increased of AMP–>cell uses more anaerobic glycolysis–>causes depletion of glycogen stores and increases in lactic acid–>decreased pH–>dysfunction of many enzymes
Consequences of Ca2+ pump failure
increased influx of Ca2+–>many damaging effects
Consequences of more than 10% of ATP loss
detachment of ribosomes from the ER and a loss in the amount of protein synthesis
Misfolding of proteins
damage to the mitochondrial and lyososomal membranes–>cell necrosis
Ways mitochondria can be damaged
decreased GFs/DNA, protein damage
increased cytosolic Ca2+
ROS
O2 deprivation, toxins, radiation
3 major consequences of mitochondrial damage
formation of mitochondrial permeability transition pore
abnormal oxphos leads to ROS
when incfreased permeability of outer mitochondrial membrane, caspases are able to leak out–>apoptosis
formation of mitochondrial permeability transition pore
high conductance channel that opens up and causes the mito to lose electrical membrane potential and no longer be able to create ATP via oxphos–>necrosis
What is a structural component of the mito transition pore?
cyclophilin D
Cyclophilin D
target in immunosuppressive drugs
cyclosporin (anti-rejection drug) blocks pores: keeps new tissues from undergoing apoptosis
3 ways increased intracellular Ca2+ can lead to cell injury
In mitochondria: causes mitochondrial permeability transition pores to open–>failure of ATP generation
in cytosol: activates enzymes that damage the cell (all from lysosomes)
intracellular Ca2+: directly activates apoptosis via caspases and increasing mito permeability
Enzymes that damage the cell from lysosomes
phospholipases
proteases
endonucleases
ATPases
How do free radicals affect cells?
attack proteins, lipids, carbs, nucleic acids
ROS
oxygen derived free radical
naturally produced during oxphos, but are degraded
oxidative stress
increased ROS; present in many diseases
What are the natural free radicals made during oxphos?
H2O2, hydroxyl ions, OH with 3 electrons
How else can free radicals be generated?
absorption of radiant energy (UV light or X rays)
leukocytes and intracellular oxidases
enzymatic metabolism of exogenous chemicals or drugs
transition metals
NO
How do leukocytes create free radicals?
use NADPH oxidase during inflammation
How do transition metals create free radicals?
iron or copper donate or accept free electrons to make ROS
iron can reduce Fe3+–>Fe2+ and the reaction is enhanced by oxygen
NO as a free radical
generated by macrophages, neurons, an endothelial cells
can act as a free radical or turn into highly reactive products (NO2, NO3)
Removal of free radicals
decay quickly on their own
antioxidants
attaching Fe and Cu to transport proteins
enzymes that break them down
Antioxidants
block free radical formation
grab onto the electron and shuttle it around–>inactivates it
Vitamin E/A, ascorbic acid, glutathione
Purpose of attaching Fe and Cu to transport proteins
transferrin, ferritin, lactoferrin, ceruloplasmin
prevents them from making free radicals
Enzymes that scavenge free radicals and break down ROS
Catalase
superoxide dismutase
glutathione peroxidase
Catalse
found in peroxisomes
H2O2–>O2 + 2 H2O
Superoxide dismutase (SOD)
convert O2 to H2O2
uses Mn-SOD as a cofactor in the mitochondria and Cu-Zn-SOD in the cytosol
Glutatione peroxidase
breaks down OH- or H2O2
can use this to look at the oxidative state of the cell (and the ability of the cell to detoxify ROS) by examining the oxidized to reduced glutathione ratio
Lipid peroxidation
Free radicals (usually OH- in the presence of O2) attack the double bonds of unsaturated FA's in the lipid membrane of cells this propagates to other lipids that surround it, via the peroxidases created
Free radicals promote:
oxidation of AA side chains
formation of protein-protein cross-linking like in the form of disulfide bonds
oxidation of protein backbone
Results of promotions of free radicals
damage active sites of enzymes
disrupt the structural conformation
enhance proteosomal degradation of unfolded proteins
Lesions of DNA
can cause single and double strand breaks in DNA, cross-linking DNA strands, formation of adducts–>cell aging and cancer
Can ROS trigger necrosis or apoptosis?
Yes, both
may also be involved in physiological factors
Pathologic effects of O2-
stimulates production of degradative enzymes in leukocytes and other cells; may directly damage lipids, proteins, DNA; acts close to the site of production
Pathologic effects of H2O2
Can be converted to -OH and OCl-, which destroy microbes and cells; can act distant from site of production
Pathologic effects of -OH
most reactive oxygen-derived free radical; principal ROS responsible for damaging lipids, proteins, and DNA
Pathologic effects of ONOO-
damages lipids, proteins, DNA
Mechanisms of membrane damage
ROS via lipid peroxidation
decreased phospholipid synthesis
increased phospholipid breakdown
cytoskeletal abnormalities
Consequences of decreased phospholipid synthesis
via hypoxia or mitochondrial dysfunction
affects all cell membranes including the membranes of the organelles
Increased phospholipid breakdown
via activation of Ca2+ dependent phospholipases
phospholipid breadown leads to an increase in lipid breakdown products (FAs, lysophospholipids)
How do fatty acids and lysophospholipids affect the cell?
detergent effect on the membrane
may insert/exchange into the membrane and change the permeability and electrophysiologic alteration
Cytoskeletal abnormalities
increased Ca2+ levels cause proteases to attack the cytoskeleton and allow it to detach from the membrane
this allows the expanding membrane to detach and stretch/rupture while it is expanding
2 morphological changes that represent irreversible changes in cell injury
inability to reverse mitochondrial dysfunction
profound problems with membrane function
Creatine kinase and troponin
biomarkers released from cardiac muscle that can be found in the blood when there is membrane damage
Alkaline phosphatase
biomarker released from liver and bile duct epithelium when there is membrane damage
Transaminases
biomarkers released from hepatocytes when there is membrane damage
Cell free DNA (cfDNA)
released into blood via different sources: primary tumor, tumor cells circulating in peripheral blood, metastsatic deposits present at different sites, and normal cell types
What happens to cfDNA during tumor development?
accumulation increases in the blood; cause d by excessive DNA release by apoptosis and necrosis
What to look for when expecting MI
troponin in blood within 2-4 hours
actin is usually wound around troponin, but once interrupt cell’s ability to maintain this, see troponin in blood
Microscopic features of MI and its repair: day 1
elonged and narrow; wide spaces between dead fibers have edema and neutrophils
Day 3-4 post MI
dense polymorphonuclear infiltrate
Days 7-10 post MI
removal of necrotic myocytes by phagocytosis
Healed MI
scar; residual cardiac M. cells have compensatory hypertrophy
Ischemia
most common type of cell injury; results from hypoxia induced by reduced blood flow
Can you have hypoxia without ischemia?
Yes, but ischemia is more rapid and severe than hypoxia without ischemia because ischemia cannot do aerobic or anaerobic glyocolysis, but hypoxia can still do anaerobic
hypoxia-inducible factor 1
transcription factor that promotes blood vessel formation, stimulates cell survival pathways, and enhances anaerobic glycolysis
Ischemia reperfusion injury mechanism
oxidative stress, intracellular Ca2+ overload, inflammation, and complement system activation
Oxidative stress due to reperfusion
increased generatin of ROS and reactive nitrogen species
produced from incomplete reduction of O2 by damaged mitochondria and by the action of oxidases in leukocytes, endothelial cells, or parenchymal cells
decreased activity of antioxidants leads to the accumulation of free radicals
Intracellular Ca2+ overload due to reperfusion
begins during acute ischemia
continues to get worse when the reperfusion happens and the blood brings lots of Ca2+ to the cell and the membrane is damaged and unable to keep it out
Ca2+ causes the pores to open in the mitochondria that makes things go down in the cell
Inflammation due to reperfusion
the surrounding cells that are dying from necrosis are releasing factors that attract immune cells (neutrophils) to come into the area and they release more damaging stuff
Complement system activation due to reperfusion
some IgM Abs deposit in ischemic tissues and cause compliment proteins to bind to deposited Abs and thus activate when reperfusion happens
How do chemicals induce cell injury?
direct toxicity to cells
conversion of the toxin to something that is able to attack the cell
Mercury (mercuric chloride)
binds to sulfhydryl groups of the cell membrane proteins–>increased membrane permeability and inhibition of ion transport
greatest damage occurs to cells that concentrate, absorb, or excrete the chemicals like the GI and kidney
Cyanide
inhibits oxphos in the mito
Antineoplastic drugs and antibiotics
are directly toxic to cells
How does conversion of the toxin to something that is able to attack the cell occur?
typically done by p450 in the ER of the liver
toxic metabolites usually do damage via formation of free radicals and subsequent lipid peroxidation AND direct bindnig to membrane proteins/lipids
CCL4 is converted to a free radical form which causes lipid peroxidation and damages cell structures
acetaminophen is made toxic in the liver–>cell injury
Apoptosis
pathway of cell death that is induced by a tightly regulated suicide program in which cells destined to die activate intrinsic enzymes that degrade the cell’s own DNA and cytoplasmic proteins
What do apoptic cells break down to?
apoptic bodies- contains portions of cytoplasm and nucleus
Does apoptosis cause inflammation?
No, because plasma memebrane is still intact and the cell is devoured by phagocytes before anything can leak out
Physiologic apoptosis
embryogenesis, hormone sensitive dependent organs with hormone withdrawal, cell loss in proliferating populations, elimination of harmful, self-reactive lymphocytes, getting rid of neutrophils in acute inflammation
Pathologic apoptosis results when there is:
DNA damage, accumulation of misfolded proteins, virus induced cell death, pathological atrophy in parenchymal organs after duct obstruction
Apoptosis morphology
cell shrinkage, chromatin condensation, formation of cytoplasmic blebs and apoptotic blebs, cells eaten by macrophages then degraded by lysosomes
What do apoptotic cells/bodies look like histologically?
very eosinophilic, can have nuclear fragments or no nuclear fragments
Caspases
cause apoptosis; cystein proteases that cleave proteins after aspartic residues; must undergo cleavage to become active
2 phases of apoptosis guided by caspases
initiation phase- caspases are enzymatically activated
execution phase- other casapses trigger degradation of cell components
Intrinsic (mitochondrial) pathway of apoptosis
Malignant cells can avoid this
increased outer mito membrane permeability and release of pro-apoptotic molecules (cyt C)
Anti-apoptotic proteins
BCL2, BLC-XL, MCL1
all contain 4 BH domains
found in the outer mito membrane, cytosol, and ER membrane
keep outer membrane impermeable
stimulated by GFs in terms of activity and production
Follicular lymphoma
neoplasm that is the result of a translocation that produces a protein from the fusion of the BLC-2 and IgH genes
Pro-apoptotic proteins
BAX and BAK contain 4 BH domains when activated (by loss of survival signals, DNA damage, etc), they oligomerize within the outer mito membrane and increase permeability
Apoptotic sensors
BAD, BIM, BID, Puma, and Noxa
only contain 1 BH domain
balance the activity of the pro and anti-apoptotic proteins
are able to sense damage like ER stress and activate pro-apoptotic proteins while blocking function and synthesis of the anti
The caspase cascade
cyt C is released into cytosol and binds to APAF-1 to form an apoptosome
apoptosome then binds to caspase 9 which is the initiator caspase of the intrinsic pathway
caspase 9 cleaves adjacent caspase 9 molecules creating an auto-amplification process which activates the executioner caspases (caspase 3/6)
Smac/Diablo
mitochondrial proteins that enter the cytoplasm and neutralize proteins (IAPs) that inhibit apoptosis
IAPs usually block caspase activation to keep the cell alive
Initiator phase: extrinsic (death-receptor initiation) apoptotic pathway
started by the activation of death domain (Fas) receptors
TNFR1 and Fas (CD95)
Fas ligand is expressed on T cells that recognize self Ags and cytotoxic T lymphocytes that kill virus infected tumor cells
Fas is on all cells
when they bind, 3+ Fas proteins come together and create a binding site for FADD
FADD then binds inactive caspase 8 and 10 and they cleave each other to activate them
proceed with intrinsic pathway
What can inhibit the extrinsic apoptotic pathway?
FLIP by binding to caspase 8 and preventing it from being cleaved
How are the intrinsic and extrinsic pathways linked?
in liver and pancreas, caspase 8 activated the BH3 protein–>feeding into the mito pathway
Execution phase of apoptosis
2 initiating pathways converge to a cascade of caspase activation, which mediated the final phase of apoptosis
intrinsic pathway activates initiator caspase 9
extrinsic pathway activates initiator caspase 8 and 10
initiator caspases will activate executioner caspases 3 and 6 which cleave an inhibitor of DNAse to chop up the DNA and degrade the nuclear matrix= promote fragmentation of nuclei
Removal of dead cells after apoptosis
bite-sized fragments for phagocytosis
changes to make sure phagocytized before start to necrose
How are phagocytes recruited after apoptosis?
phosphatidylserine flips to outer PM
secrete soluble factors
apoptotic cells coat in thrombospondin which stick to the coating produced by phagocytes
coating of C1q
What causes apoptosis?
GF deprivation DNA damage protein misfolding TNF receptor family CTL killing of cells
GF deprivation in apoptosis
hormone sensitive cells deprived of relevent hormone
lymphocytes not stimulate any Ags and cytokines
neurons deprived of nerve GF
intrinsic pathway
DNA damage causing apoptosis
radiation or chemo
p53 accumulates and arrest the cell cycle in G1 to allow the cell to repair the DNA
if that doesn’t work–>apoptosis
TP53 gene
makes the p53 protein that binds to DNA
causes cell cycle arrest and apoptosis in response to DNA damage
if mutated/absent, cells with damaged DNA survive–>neoplastic mutation transformation
mutated in Li-Fraumeni syndrome to cause diverse cancers
Protein misfolding leading to apoptosis
if unfolded/misfolded proteins accumulate in ER because of genetic mutations, aging, environment, neurodegenerative disease, and T2D–>unfolded protein response
Unfolded protein response
increased production of chaperones
enhanced proteosomal degradation of abnormal proteins
slow protein translation
if cell cannot do this, will activate apoptosis- ER stress
ER stress
protein folding demand»_space; protein folding capacity
Apoptosis induced by the TNF receptor fam
FasL on T cells bind to Fas on the same/neighboring lymphocytes
this rids lymphocytes that recognize self-ags and mutations in Fas/FasL in autoimmune diseases
CTL killing of cells
CTLS recognize foreign Ags on infected host cells
use FasL on the T cell to bind activate Fas on other cell
The activation causes the cell to undergo apoptosis and for the T cell to secrete perforin
Perforin creates pores that allow proteases called granzymes to enter the cell and cleave proteins at aspartate residues which activates caspsases for apoptosis
What is the most common mutation in human cancer?
TP53 mutations
Disorders associated with increased apoptosis and excessive cell death
neurodegenerative diseases from loss of neurons due to misfolded proteins and genetic mutations
ischemic injury
death of virus infected cells
Cystic fibrosis
Caused by misfolded proteins
loss of CFTR leads to defects in Cl- transport
Familial hypercholesterolemia
Caused by misfolded proteins
Loss of LDL receptor leading to hypercholesterolemia
Tay-Sachs disease
caused by misfoled proteins
Lack of the lysosomal enzyme leads to storage of GM2 gangliosides in neurons
Alpha-I-antitrypsin deficiency
caused by misfolded proteins
storage of nonfunctional protein in hepatocytes cause apoptosis; absence of enzymatic activity in lungs causes destruction of elastic tissue giving rise to emphysema
Creutzfield-Jacob disease
caused by misfolded proteins
Abnormal folding of prions causes neuronal cell death
Alzheimer Disease
abnormal folding of A beta peptides cause aggregation within neurons and apoptosis
Necroptosis
form of cell death that shares aspects of necrosis and apoptosis
Necroptosis morphology
loss of ATP, swelling of cell/organelles, generation of ROS, release of lysosomal enzymes, eventual rupture of the membrane
Necroptosis mechanism
Genetically programmed (like apoptosis)
does not result in activation of caspases
activated by ligation of a receptor
TNFR1 is the best example as it can do both apoptosis and necrosis
can also be triggered by Fas, viral D/RNA sensors, and genotoxic agents
RIP1 and 3
unique kinases to necroptosis that are recruited upon ligand binding of TNF to TNFR1
TNFR1 and RIP1/3 when TNF binds
form a complex that contains caspase 8
if caspase 8 is active–>apoptosis
if caspase 8 is not active–>permeabilization of lysosmal membranes, generation of ROS, damage to mitochondria, reduction of ATP–>necroptosis
Physiological functions of necroptosis
occurs in the formation of the bone growth plate
works as a backup for viruses that encode caspase inhibitors
Pyropoptosis
accompanied by fever induced IL-1
microbe products enter the cytoplasm and activate the inflammasome, which can then activate caspase 1 (IL-1B) by cleaving the precursor IL-1
caspase 1 and 11 then work together to kill the cell
good for killing some microbes that enter the cytoplasm
Morphology of pyropoptosis
swelling of cells, loss of PM integrity, and release of inflammatory mediators
Autophagy
process in which the cell eats its own contents
What is the purpose of autophagy?
used to save the cell during starvation, clean up debris, turn over cell organelles, and recycle critical nutrients
In what type of cell is autphagy prominent?
atrophic cells, which are exposed to severe nutrient deprivation
3 ways autophagy can trigger cell death
Chaperone mediated
Microautophagy
Macroautphagy
Chaperone mediated autophagey
the translocation of stuff into the lysosomes is directly done by chaperone proteins
Microautphagy
inward invagination of the lysosomal membrane for delivery
Macroautophagy
aka autophagy; portions of the cytosol are placed in a double membrane autophagic vacuole kown as an autophagosome
Autophagy mechanism
formation of an isolation membrane (phagopore) from the ER
Elongation of the vesicle
Maturation into the autophagosome–>fusion with endosome and then lysosome–>autophagolysosome–>degredation of contents by lysosomal enzymes
Phagopore
nucleation complex from the ER that is promoted by starvation and lack of GFs
Elongation of the vesicle involves…
vesicle elongates, captures cytosolic cargo, and closes to form the autophagosome
requires ubiquitin-like systems using microtubule associated protein light chain 3 (LC3) which is a useful marker for finding cells doing autophagy
LC3 helps select the contents from the cytosol that should be eaten in times of low food
What is autophagy involved in?
turnover of ER, mito, lysosomes
triggering death if cell not coping with stress
cancer: can promote or inhibit growth depending on the cell/cancer
Neurodegenerative disorders
Infectious diseases
IBD’s
Neurodegenerative disorders and autophagy
associated with dysregulation of autophagy
in Alzheimer’s disease, autophagy is accelerated
In Huntington’s disease, the mutant huntington impairs autophagy
Parkinson’s
Infectious diseases and autopahgy
many pathogens are degraded by autophagy, as this is one way to present Ags to the immune system
deletion of Atg5 in macrophages increases the susceptibility of TB
IBDs and autophagy
Crohn’s disease and ulcerative colitis are linked to SNPs in autophagy related genes
Intracellular accumulation
accumulation of abnormal amounts of harmless/harmful substances in cytoplasm, organelles, nucleus
4 main pathways of intracellular accumulation
Inadequate removal of a normal substance due to defects in packaging and transport
Accumulation of an abnormal endogenous substance as a result of genetic or acquired defects in folding, packaging, transport, or secretion
failure to degrade a metabolite due to inherited enzyme deficiencies
deposition and accumulation of abnormal exogenous substance when the cell is not able to digest or move it
Accumulation of lipids intracellularly are due to
from an abnormal metabolism
TAGs, cholesterol, phosopholipids (myelin figures)
occurs in lysosomal storage disease
Steatosis
fatty change
abnormal accumulation of TAGs within parenchymal cells
often seen in liver since it does a lot with fat metabolism, but also occurs in the heart, kidney, and muscle tissue
Cholesterol and cholesterol esters
cells use cholesterol for membrane synthesis, but not accumulation
Atherosclerosis
in atherosclerotic plaques, smooth muscle cells and macrophages within the intima layer of IgA’s fill with lipid vacuoles contain cholesterol and cholesterol ester
Foam cells
appear yellow and foamy
form from smooth muscle cells and macrophages within the intima layer of IgA’s that fill with lipid vacuoles containing cholesterol and cholesterol esters
What happens when foam cells rupture?
lipids go into extracellular space–> crystallize
Xanthomas
clusters of foam cells (often macrophages) that accumulate in the subepithelial CT of the skin and in tendons that form tumors
Cholesterolosis
accumulation of foam cells macrophages in the lamina propria of the gallblader
Niemann-Pick disease Type C
lysosomal storage disease that affects an enzyme that moves cholesterol around
results in cholesterol accumulation in lots of organs
Protein intracellular accumulation
defect in protein folding/transport
Morphology of protein accumulation
intracellular accumulations of protein appear as rounded, eosinophilic droplets, vacuoles, or aggregates in the cytoplasm
by EM, they are amorphous, fibrillar, or crystalline
Causes of protein intracellular accumulation
reabsorption droplets in proximal renal tubules
Russell bodies
defective intracellular transport and secretion of critical proteins
accumulation of cytoskeletal proteins
aggregation of abnormal proteins
Reabsorption droplets in proximal renal tubules
seen in renal diseases that have proteinuria
if the glomerulus lets many proteins into the filtrate, it reabsorbs it via pinocytosis in PT into vesicles–>the protein appears as pink hyaline droplets within the cytoplasm of PT cells
reversible if the proteinuria diminishes and the droplets are allowed to be metabolized
Russell bodies
in cells that are producing lots of cells very quickly, like in synthesis of Igs in plasma cells, then the ER becomes very distended and produces large, homogenous eosinophilic inclusions
Defective intracellular transport and secretion of critical proteins
in alpha1-antitrypsin deficiency, mutations in the protein–>slow folding–>buildup of partially folded intermediates in cell and not secreted
the pathology comes from both the lack of protein (that causes emphysema) and from apoptosis due to ER stress
accumulation of cytoskeletal proteins
accumulation of keratin filaments and neurofilaments are associated with cell injury
In alzheimer’s, the neurofibrillary tangle found in the brain contains neurofilaments and other proteins
Alcoholic hyaline
an eosinophilic cytoplasmic inclusion in liver cells that is commonly seen in alcoholic liver disease
there is an accumulation of keratin intermediate filaments in the cells
Aggregation of abnormal proteins
abnormal or misfolded proteins may deposit intracellularly, extracellulary, or both
cause direct or indirect effects
certain forms of amyloidosis fall into this category
these conditions are also called proteinopathies or protein-aggregation diseases
