LECTURE 7: MECHANISMS OF CELL DEATH AND TISSUE REPAIR Flashcards
WHY DO WE CARE ABOUT CELL INJURY?
Homeostasis: Cell is at optimal function, meeting physiologic demands
Adaptation: Reversible changes in response to cells environment
Cell Injury: Cells cannot adapt, or the max adaptive response to stimuli is exceeded
Cell Death: State in which cell ceases to carry out functions
CELL INJURY
Factors affecting cell injury
§ Nature, duration, severity
§ Cell type and adaptability
§ Activation of multiple mechanisms
Types cell injury
§ Reversible
§ Irreversible
- Chemical Injury
Many mechanisms
▫ Some directly target organelles
▫ Some require metabolic activation
▫ Some trigger an inflammatory response
▫ Often very selective – based on kinetics
- Free Radicals/Reactive Chemicals
Normal Metabolism
Reactive Metabolites
O2
- ·
OH ·
H2O2
Cellular Damage
Cell Membrane
Mitochondria
ER
DNA
Proteins
SOD/Catalase
Glutathione Peroxidase/GSSG
Under normal metabolism
we generate reactive metabolites, such as super oxide hydroxide, hydrogen peroxide. These, under normal conditions, actually play a role in in endogenous systems in time and a sigline.
If you have overproduction, we react to metabolites.
you can have an antioxidant system within the cell.
such as sods, superoxide, discontase, or catalyzed and removed some of those reactive
free radicals.
What happens when there’s too much damage, too much generation of free radicals or reactive metabolites in that antioxidant system becomes overcome. You get cellular damage. You get various things that can occur. You can have impact cell memory changes in liquid per oxidation. We could get impact on mitochondria
you can get DNA damage and oxidize DNA just to resolve and dissolution so, or you can impact your proteins
- Infections
- Variety of mechanisms that destroy host cells
and tissues
For example: - Bacterial toxins – lytic phospholipases
- Viral replication – promotes cell lysis
- Immunologic diseases
Immune system has several different molecular
mechanisms of cell killing
▫ Innate or Adaptive Response
* Hypersensitivity – overblown exaggerated immune
response
* Autoimmunity – Your own cells recognized as foreign
- Hypoxic Injury
- Hypoxia means the tissues are starved of oxygen
- Ischemia means blood flow is cut off to the tissue
(blockage of coronary artery) - A mild ischemic/hypoxic injury is reversible if tissue
oxygen supply is restored - If the injury is severe or prolonged, the cell is damaged
irreversibly and dies
DIFFERENCE: ischemia, not only limiting the auction of blood delivery to the target area and target tissue. But you’re also preventing removal of the metabolic waste.
Reversible cell injury
- Milder insult or shorter duration
- Subcellular mechanisms vary
Example: Stunned or hibernating
myocardium
Loss of blood flow and oxygen
↓ATP
↓Ion Pumps
(Na+/K+-ATPase, cell swelling)
↑Glycolysis -↓pH
Synthesis/storage disruption
Irreversible cell injury
Membrane
Injury
Calcium Influx
Lysosome
Breakdown
Autodigestion
Irreversible cell injury
Protein released
(markers of injury)
If ischemic event is pro long too far, or Toxicant too overcoming for the cell? It’s an irreversible point.
in this irreversible injury we get a lot of memory that we start to see lost membranes. membrane functions can impact the membrane in proteins.
This calcium is going to activate various different
casting, dependent enzymes to start breaking down and degrading.
, as you start to lose this function of membrane, you can get release of protein markers. You’re looking for markers that have been released from the cell types that can help you indicate.
Mechanism of cell injury
§ Mitochondrial damage
§ Abnormal calcium homeostasis
§ DNA damage
§ Membrane damage
§ ER Stress
§ Oxidative stress
mitochondria part of the major source of reactive option species production.
In addition, they actually activate cell death pathway, apoptosis, atophagy, necroptosis
example, abnormal calcium. Since you start getting a calcium overload and damage mitochondria, which is a storage source for mitochondira, activation of degredation
if you have er damage, you’re going to get a lot of misfolded proteins and a lot of subsequent problems
cell injury
cellular components
biopsy
enzyme release
Cellular components
▫ Water, Lipids, Proteins, DNA, Pigments
▫ Ions: calcium, sodium, potassium
Biopsy
▫ Liver, lung, kidney, GI tract, skin
Enzyme release
▫ Heart: Myoglobin, CK-MB, Troponin, LDH, BNP
▫ Liver: AST, ALT, LDH, Alkaline Phosphatase
▫ Pancreas: Amylase, Lipase
CELL DEATH
“Cell death: is the point at which the cell becomes unable to recover
its normal morphology and function even if all processes leading to
its dissolution are stopped.”
3 distinct routes of cellular catabolism defined morphologically
apoptosis
autophagy
necrosis
Necrosis
1. Accidental necrosis:
2. Necropoptosis
Accidental Necrosis (passive process)
* Pathological (noxious stimuli)
* Occurs synchronously in multiple cells
* Early loss of membrane integrity
* Generalized cell and nuclear swelling
* Nuclear chromatin disintegration
* Inflammatory reactions
* Energy independent (dramatic irreversible drop in ATP)
* Historically regarded as unregulated cell death
, changes in and ion concentrations and water is going to come in. The cells start to swell.
Trigger inflamm response - loss of membrane integrety, intracellular stuff spreads in surrounding env to activate immune response
Exaggerated repsonse = more cell death, injury
Morphological Descriptions
When many cells undergo necrosis at once,
definable patterns are produced
- Coagulative necrosis
- Infarct necrosis
- Liquefactive necrosis
- Fatty necrosis
- Caseous necrosis
Coagulative necrosis
* Infarct necrosis
Infarction – necrosis caused by ischemia or anoxia (heart attack/stroke).
Tissue shows red stain indicating clot proteins (ie., fibrin), anoxic injury.
Loss of blood supply
Infarct - necrotic or dead tissue
Clotting factors from injury
We can see the dead white by the infarcted tissue
and see a rupture occurred over the 3’clock position.
Liquefactive- necrosis
Neuronal-brain
Fluid remains following digestion of necrotic tissue.
Left 0 can see a cavity and dead tissue surrounding
you’re getting the release of a monolithic enzymes. And you basically starting to degrade the surrounding tissue in the space. In basically of liquid formation.
you’re getting loss of blood supply. You’re not removing any of the the infarct tissue
and the damage tissue you can build up.
Caseous - necrosis
Lung - tuberculosis
Caseous - necrosis
Combination of coagulative and liquefactive necrosis
Granulomas - Immune response
Fatty - necrosis
“Production of soaps”
“Necrotic Fat Cells”
Leak of digestive enzymes – lipase
Release of fatty acids combine with minerals
The next is the fatty necrosis, and this results from the action. Of lipases in fat tissues
The pancreas releases enzymes, the lipases digest fat which causes production of soaps (soft appearances)
We see a loss in membrane integrity, cell can’t be defined, promoting a fat formation basically
“Programmed Cell Death”
Apoptosis
- Active process that depends on the execution of a
defined sequence of signaling events - Dependent on genetically encoded signals or activities
- Note:
‘programmed cell death’ and ‘apoptosis’ are not
synonyms - Coined by Kerr et al (1972) –
described a morphological aspect of
cell death - Critical in the maintenance of normal
organ and tissue homeostasis - Removal of damaged, senescent or
unwanted cells - Important role in sculpting
development (nervous system) and
maintaining normal function of
immune system
The next is the fatty necrosis, and this results from the action. Of lipases in fat tissues
The pancreas releases enzymes, the lipases digest fat which causes production of soaps (soft appearances)
We see a loss in membrane integrity, cell can’t be defined, promoting a fat formation basically
Apoptosis (active process)
- Physiological or pathological
- Asynchronous process in single cells
- Genetically controlled
- Cell rounding up, reduction of volume
- Condensation of nuclear contents (DNA laddering)
- Late loss of membrane integrity and little ultrastructural
damage to cytoplasmic organelles - Evokes little inflammatory response
- Energy dependent
A unique feature is this can occur in a single cell
a unique feature is, you get the condensation of the contents
traditionally. What they used to do to analyze the optos as you take your DNA, you write it out on a gel, and you basically get what looks like a ladder. There is a series of different DNA fragments. And what’s happening is as you start breaking down your DNA, you start cleaning it
at sites that wrap around the promotion
It’s a late loss of memory integrity.
Often requires a lot of ATP
Autophagy
Ø Self-digestive process
Ø Cytoplasmic and intra-cellular organelles sequestered into double
membrane vesicles
Ø Fuse with lysosomes for digestion
Ø Does not display chromatin condensation
Ø Caspase-independent
Ø 3 major categories (1) Macroautophagy
(2) Microautophagy
(3) Chaperone-Mediated Autophagy
Misleading process often associated with cell survival
* Nutrient deprivation – triggers process
* Activity enables cells to restore sufficient energy levels
and promotes viability
* Paradoxically- ‘point-of-no-return’ - extensive activation
can result in cell death
Lysosome mediated processes
it’s a self digestive process to remove damage proteins or organelles
if you have like serial starvation or that damage protein
organelles, it’s going to activate a process
to form a double membrane around that organelle that’s basically a fuse with a lysosome for digestion.
Autophagy does not display chromatin condensation
Cell Death - Summary
- Existence of multiple cell death pathways - complex
- Inhibition or removal of key molecules in cell death pathway does
always not prevent cell death - Cells still die but differently
- Understanding of the molecular and biochemical regulation of cell
death – key in developing novel therapeutic agents
What happens after cells and tissues are
damaged?
Tissue repair
* Phagocytes clean up the debris.
* New blood vessels grow in.
* Some tissues may regenerate.
* Scarring may occur
You have your initial major event, you can have clot formation, hemostasis So a major event. You get a cut.
We get an injury on chemical burn
Neutrophils, macrophages come in, lymphicytes, fibroblasts
ou can think of that initial phase in that first week is really that inflammatory response that is occurring.
The second is going to shift the information proliferation. proliferating a lot of fibroblasts.
and that remodeling machine after the first 3 weeks in a month to a year
Cleaning up the debris
- Early stages, area ‘cleaned up’ by
phagocytosis – WBC (neutrophils) - Occurs within minutes
- Over few days – phagocytes begin to
accumulate (macrophages derived from
monocytes)
Early Tissue repair
Over a few days, tissue scaffold begins to repair
* New growth of tiny blood vessels (endothelial cells) –
provide blood supply for reconstruction
* Proliferating blood vessels – meshwork of tiny capillaries
= granulation tissue
* Several days post-injury
Late Tissue repair
- Fibrous tissue = scar
- Fibroblasts – proliferate and synthesize collagen – tough
fibrous protein which binds together (scar) - Days to weeks
- Some tissues can regenerate (liver, skin)
- Some have no regenerative capacity (heart muscle,
CNS – however evidence this may not be completely
true)
How do tissues respond to abnormal
physiologic stresses?
Tissue adaptations
- Cells can respond in other ways to stresses created by
disease states or physiologic overload
Metabolic Responses
- hydrophobic swelling
- fatty acid change
- protein accumulation
Growth Responses
- atrophy
- hypertrophy
- hyperplasia
- metaplasia
apoptosis diagram
KEY MESSAGE:
There’s 2 central pathways. There’s an intrinsic pathway that involves the mitochondria
and an extrinsic pathway that is resulting from extracellular signal and receptor mediatedpathway.
Key players are caspase enzymes involved with catalytic degredation
Mitochondria, ER play important role
Results in DNA fragmentation
autophagy diagram
3 types
Macroautophagy: Double membrane, going to expand and surround the oranelle of proteins that need ot be removed.
You can form this autofagos on
it will fuse with your lysosome, the contents will be degraded, and you get efflux
Chaperone:
involve specific protein, such as Lr. P. 2, a. His own 70 basically binding the specific motif on a protein is basically a targeted translocated
to the lysosome where it will be degraded in this vacuum, metabloties removed or reuptaken into cell
Microautophagy: specific organelle (damage mitochonria), ggoing to target damage in mitochondria and fuse with lysosome for degredation and removal
You can get an atrophy, this muscles, for example, on your leg and maybe get smaller. Once you start using them more and get more blood flow, regain muscle strength
Hypertrophy getting bigger muscle, stop working will decrease in size
. hyperplasia is an increase in cell number, so you have inflammatory, immune response. You can be producing have generation more cells.
We remove the stimuli. We can basically reduce the cell number.
Metaplasia: changing cell type, acid reflux
Esophageal cells convert due to acid
