cell injury and inflamm and healing and repair (Lec 3+4) Flashcards
Causes of cell stress and injury
1* Physical injury: e.g. trauma, heat, cold, radiation, electricity, and oxygen deprivation.
2* Chemical injury: e.g. pH extremes, free radicals, low or high oxygen concentration, poisons, drugs
3* Biological causes: e.g. factors arising from micro-organisms, damaging factors released during immune responses, nutritional imbalances, lack of growth factors.
4* Immunologic injury (e.g. in autoimmune reactions).
5* Genetic derangements range from severe congenital malformations to subtle variations in
the genetic makeup that influence the susceptibility of cells to injury.
6* Nutritional imbalances range from severe protein-calorie deficiencies in third world
starvation or anorexia nervosa to excess intake of lipids and cholesterol predisposing to atherosclerosis.
What happens to cells when there is injurious stimulus (what is affected)
LEARN FLOWCHART DIAGRAM
This occurs at the same time:
1. Loss of ATP
= loss of energy dependent cellular functions
- Membrane damage:
- affects mitchondria (causing that loss of ATP) leading to cell death
- lyosome causing enzymatic digestion of cellular components
-plasma membrane cuasing loss of cellular contents - Increased intracellular Ca AND reactive oxygen species = Protein and DNA breakdown
- Reduced energy production
- what is the effects of this on the cell (particulary effects on DNA, pumps and protein synthesis)
Depletion of ATP commonly occurs during cell injury – e.g.
-due to lack of oxygen -damage to enzymes in the cytoplasm
-damage to mitochondrial
NO ATP PRODUCTION =
1. This reduces the energy available to enzymes that repair damaged DNA and proteins.
- This also reduces the energy available for ATP-driven membrane ion pumps.
- Na+ pump activity reduced causing Na and water to accumulate causing cell swelling
-Ca2+ pump acitivity decreased causing influx of Ca2+ ions into cytosol causing activation of destructive calcium dependent enzymes
Overall, these pumps control the ionic and osmotic homeostasis of the cell and its organelles.
- Reduces the energy available for protein synthesis and causes detachment of ribosomes from the rough endoplasmic reticulum.
(2) Damage to cell membranes
-Why does this happen?
-
This may occur directly (e.g. due to free radicals), following hypoxia (stress due to lack of oxygen), due to membrane-targeting bacterial toxins (e.g. the a-toxin of Clostridium perfringens) or following failure of the plasma membrane Ca2+ pump
Damage to cell membranes:
Results in?
Damage to lysosome membrane results in?
Damage to mitochondrial membrane results in?
Plasma membrane damage results in
- loss of cellular contents
-loss of osmotic balance
- influx of fluids and ions
-loss of proteins, enzymes, coenzymes, and ribonucleic acids.
Injury to lysosomal membranes results in leakage of their enzymes into the cytoplasm and digestion of cellular components – this digestion is known as autolysis.
Mitochondrial membrane damage results in Formation of nonselective high- conductance channels in the inner mitochondrial membrane.
This causes…
(1) Removes the transmembrane potential and cytochrome C required for oxidative phosphorylation
(2) Allows leakage of cytochrome C into the cytosol -> primes cells for apoptosis
(3) Increased cytosolic calcium concentration
-how does Ca increase
-what destructive calcium-dependant enzymes are activated by high ca and what does it cause
Reduced activity of the plasma membrane Ca2+ pump allows influx of Ca2+ into the cytosol (damaged cell membranes become more permeable allowing an influx of extracellular calcium and/or causing the release of calcium from intracellular stores), which activates destructive calcium-dependant enzymes such as:
- ATPases (thereby hastening ATP depletion)
- Phospholipases (which cause damage to lipid components of membranes)
- Proteases (which break down both membrane and cytoskeletal proteins)
- Endonucleases (which are responsible for DNA and chromatin fragmentation)
Lecture Slide for diagram
- Damage due to free radicals
- examples of free radicals
-examples of causes of free radicals
- what damage does radicals cause
- Why do they form a cascade effect?
-how does the cell protect against free radicals
O2, H2 O2, OH, NO
Radicals cause oxidative stress
Free radicals are generated by
irradiation
Metabolsim of chemicals or drugs
oxygen toxicity
inflammation
reperfusion
effects:
-Attack double bond in unsaturated fatty acids (causes lipid peroxidation)
- Oxidise amino acid side chains (causing enzyme damage)
-React with thymine (causing DNA damage)
The initial damage they cause leads to autocatalytic reactions, whereby molecules with which they react are themselves converted into free radicals to propagate a chain of damage.
Cells have defense systems to prevent injury caused by free radicals including; 1. antioxidants (e.g. vitamins E and A in membranes
2. ascorbic acid
3. glutathione in the cytosol)
4. enzymes such as catalase, superoxide dismutases and glutathione peroxidases.
- Damage to proteins
- how can they be damaged?
- Direct damage
- by free radicals
- calcium-dependant protease enzymes and targeted for degradation. - Proteins may also be damaged by glycation (the addition of sugar residues) – e.g. in diabetes, neurodegenerative disorders and cataracts.
- Damage to cytoskeletal proteins may detach the cell membrane from the cytoskeleton
(6) Damage to nuclear or mitochondrial DNA.
- examples of reagents that cause this
- Ionizing radiation (e.g. X-rays and gamma rays) has sufficient energy to break chemical bonds and may cause DNA strand breaks.
- Ultraviolet radiation causes structural changes in DNA bases that may eventually lead to cell death (e.g. in sunburn).
- Chemical agents (mutagens) and free radicals
- Genetic causes – e.g. mutations in the ATM gene reduce DNA repair after damage and
predispose to cancer. - Nutritional deficiencies of vitamin B12 or folate affect DNA synthesis.
How do cells respond to stress or injury that is IRREVERSIBLE
Apoptosis or neocrosis
Necrosis (outright killed)
- key features of necrosis
DOESNT need energy (passive form of cells death)
-There is lysosomal membrane rupture and leakage of
lysosomal enzymes into the cytosol which digest cellular components
(autolysis).
Cytosolic contents also leak across the damaged plasma membrane into the
extracellular space inducing an inflammatory
response
Creates featureless cytoplasm
Drug Trastuzmab
- what receptor is it ass with it
-where is it found/ass cancer -increases what signalling pathway
- what does Trastuzmab bind to
Her2 is a receptor on the surface of epithelial cells that turns on intracellular signaling pathways (including the PI3K and MAPK pathways)
In 20-30% of breast cancers the Her2 gene is ‘amplified’, leading to increased PI3K and MAPK signaling pathway activity, which turns on cancer cell division and tumour growth. Trastuzumab is much more likely to be effective in those tumours in which the Her2 gene is amplified
The drug trastuzumab (herceptin) is an artificially produced antibody that targets the Her2 receptor
How does Trastuzumab target cancer cell
- Causing Her2 receptor lysosomal degradation
- Blocking Her2 PI3K/AKT intracellular signaling
- Encouraging immune attack
Cell stress and injury leads to what outcomes?
Draw flowchart
Injury/stress
= No effect
=Adaption
= Cell injury = Irreversible (=Cell death) OR Reversible
Lecture Slide
EXAMPLE of cells that have no affect now from stimulus
Neutrophils are relatively unaffected by moderately hostile tissue environments
They have to be because they are the first responders to an event and therefore face many different environment types and stimulus
When does Cell adaption occur? AND how does cells adapt to chronic stress
MILD stress or injurious agents
Cells will…
1. Hypertrophy and Hyperplasia
hyperplasia (increased number of cells) or hypertrophy (increased size of individual cells)
2. Atrophy
Cells respond to reduced functional demands, reduced supply of nutrients and growth factors or reduced stimulation through nerves by atrophy (cell shrinkage).
3.Metaplasia (change form of cell from one type to another. Eg: oesophagus cells change to stomach like cells when there is chronic acid stimulus as stomach cells are more capable of handling acidic pH)
What are two examples of signalling pathways activated by cell stress/injury
- Heat shock factors
- they are transcription factors that induce the expression
of heat shock proteins
- Heat shock proteins are molecular chaperones that assist in the repair of damaged proteins in the cell - Stress enzymes
-the p38 MAP kinase and Jun N-terminal kinase enzymes initiate phosphorylation cascades (amplifiy a response)
- p53 activated by DNA damage -> halts cell division to allow repair or induces cell suicide
- BMF (actin cytoskeleton damage), Bim (microtubule damage), Bad (cell stress due to inadequate stimulation by growth factors)
Apoptosis (programmed cell death)
- energy needed?
- Characteristic appearnace?
-how is the mess cleaned up?
-2 pathways?
- Although the cell is irreversibly damaged, it still has the time and energy required to execute a suicide program
- It requires energy
- Characteristic appearance (membrane blebs, shrinkage, pyknosis)
- Results in phagocytosis by passing macrophages or neighbouring cells
- 2 pathways for apoptosis initiation (mitochondria and death receptors) cause activation of a cascade of upstream caspases
- Both pathways feed down into a cascade of caspase enzymes known as
executioner caspases
What is inflammation
and triggers
Inflammation is the body’s immediate response to tissue injury
- Infections (bacterial, viral, parasitic) and microbial toxins
- Trauma (blunt and penetrating)
- Physical and chemical agents
- Tissue necrosis (from any cause)
- Foreign bodies (splinters, dirt, sutures)
- Immune reactions (also called hypersensitivity reactions)
Stages of ACUTE inflammation
1) Triggering
Following tissue injury, pro-inflammatory substances are released from injured and necrotic cells.These substances activate resident tissue macrophages and the endothelial cells that line local blood vessels. Realse cytokines, histamine and prostaglandins that activate endothelial cells and also cause vasodilation
2) Blood flow and permeability changes
The activated endothelial cells then produce inflammatory cytokines, prostoglandins and nitric oxide which cause vasodilatation and increased permeability of blood vessels in the injured tissue
This increases blood flow to the damaged tissue hyperaemia and increases the flow of proteinrich fluid out of vessels into the damaged tissue exudation. The accumulatiuon of fluid in the inflamed tissue due to exudation is referred to as oedema. Fluid exudate contains a number of proteins that play an important role in the inflammatory response, including antibodies, fibrinogen and proteins of the complement, kinin and plasmin cascades which act as important chemical mediators. Fibrinogen plays an important role in inflammation it is enzymatically converted into fibrin which acts as a glue to seal damaged blood vessels and stabilise damaged tissues. Fibrin accumulates on epithelial surfaces such as the pericardium or pleura where it becomes compacted by organ movement into a dense fibrinoue exudate
3) Endothelial cell signalling and gene expression changes including adhesion molecule regulation
The expresion of cell adhesion molecules on the endothelial cell luminal surfaces is increased.
a. First, the increased expression of endothelial selectin molecules slows the flow of neutrophils by causing them to roll slowly along the endothelial cell surface. Selectins do this by binding to glycoprotein receptors on the surface of neutrophils. This rolling is analagous to a tennis ball the neutrophils rolling very slowly along a velcro surface the endothelial cells.
The expression and avidity of integrin cell adhesion molecules on neutrophils is then increased. Integrins bind to ligands known as addressins on the endothelial cells, causing the neutrophils to stop rolling and adhere firmly.
4) Neutrophil signalling and gene expression changes, neutrophil adhesion to endothelial cells and migration into tissues
The neutrophils then move between the endothelial cells into the tissues known as diapaedesis. They do this by inserting extended cell processes into the junctions between the endothelial cells, and then squeeze through the inter-endothelial junctions to assume a position between the endothelial cells and the basement membrane. Eventually, they traverse the basement membrane and escape into the extravascular space.
The loss of fluid form the vessels increases blood viscosity and slows blood flow, a condition termed stasis.
As stasis develops, leukocytes are found near the edges of the blood flow, rather than in their usual central position. This is referred to as margination. This allows leukocytes principally neutrophils which are the most common leukocyte type in the blood to accumulate along the vascular endothelium. This occurs especially in post-capillary venules.
5) Neutrophil activation, survival, function and death
Once in the injured tissue neutrophils migrate toward the site of injury by moving up gradients of chemotactic factors. This migration is known as chemotaxis. Chemotactic factors include:
c. Exogenous substances such as bacterial products that possess an N-formyl- methionine terminal amino acid.
d. Endogenous substances such as components of the complement system C5a, leukotrienes, and chemokines e.g. IL-8.
6) Either:
* Inflammation subsides
* Inflammation continues with other leukocyte types
entering the tissue (chronic inflammation)
What does endothelial cells release to encourage neutrophil migration
TNF-a -> TNF receptor -> NFkB transcription factor -> other genes -> neutrophil adhesion and passage into tissues
Inflammation-associated gene expression and signaling changes in endothelial cells
- Cell adhesion molecules INCREASE
- Anti-apoptosis molecules INCREASE
- Cytoskeleton stabilizers DECREASE
- Cytokines and Chemokines INCREASE
- Coagulation factors INCREASE
- Pro-angiogenesis factors INCREASE
- Many signaling molecules INCREASE and DECREASE
Blood flow and permeability changes during inflammation
(1) Increased blood flow = hyperaemia
(2) Loss of fluid and protein = exudation
(3) Fibrinous exudate and tissue oedema
(4) Stasis and leukocyte margination in post-capillary venules
Draw a diagram showing Neutrophil adhesion and migration into tissues
Lecture Slide
