Apoptosis and Cell Necrosis

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Apoptosis and Cell

Necrosis

Group 5

Mallare, Melvin

Manabat, Armand Jeric

Manalang, Kerwin

Manalili, Maria Minerva

Manarang, Grace Haziel

Mancia, Chester


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APOPTOSIS

programmed cell death

is a normal component of the

development and health of multicellular

organisms.

is a process in which cells play an active

role in their own death.


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Biochemical events lead to characteristic cellchanges (morphology) and death.

blebbing loss ofcell membrane asymmetry and

attachment

cell shrinkage

nuclearfragmentation

chromatin condensation

chromosomalDNA fragmentation.
http://en.wikipedia.org/wiki/Biochemicalhttp://en.wikipedia.org/wiki/Morphology_(biology)http://en.wikipedia.org/wiki/Bleb_(cell_biology)http://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Chromatin_condensationhttp://en.wikipedia.org/wiki/Chromosomehttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Chromosomehttp://en.wikipedia.org/wiki/Chromatin_condensationhttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Bleb_(cell_biology)http://en.wikipedia.org/wiki/Morphology_(biology)http://en.wikipedia.org/wiki/Biochemical


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(A). Typically, the cell begins to shrink

following the cleavage of lamins and actin

filaments in the cytoskeleton


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(B). The breakdown of chromatin in thenucleus often leads to nuclear

condensation and in many cases the

nuclei of apoptotic cells take on a "horse-

shoe" like appearance


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(C) Cells continue to shrink


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The end stages of apoptosis are often

characterized by the appearance of

membrane blebs (D) or blisters process.

Small vesicles called apoptotic bodies arealso sometimes observed


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There are a number of mechanisms

through which apoptosis can be induced in

cells. The sensitivity of cells to any ofthese stimuli can vary depending on a

number of factors such as the expression

of pro- and anti-apoptotic proteins .


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This prevents nearby phagocytes from

locating and engulfing the dead cells

caused by external factors, such as

infection, toxins or trauma.
http://en.wikipedia.org/wiki/Phagocytehttp://en.wikipedia.org/wiki/Phagocyte


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APOPTOSIS NECROSIS

NATURAL YES NO

EFFECTS BENEFICIAL DETRIMENTAL

Physiological or

pathological

Always pathological

Single cells Sheets of cells

Energy dependent

Energy independent

Cell shrinkage Cell swelling

Membrane integrity

maintained

Membrane integrity lost


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APOPTOSIS NECROSIS

Role for mitochondria and cytochrome

C

No role for mitochondria

No leak of lysosomal enzymes Leak of lysosomal enzymes

Characteristic nuclear changes Nuclei lost

Apoptotic bodies form Do not form

DNA cleavage No DNA cleavage

Activation of specific proteases No activation

Regulatable process Not regulated

Evolutionarily conserved Not conserved

Dead cells ingested by neighbouring

cells

Dead cells ingested by neutrophils and

macrophages


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Internal Mechanism


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Caspases

Caspases are cysteine proteases that

cleave peptide bonds next to an aspartate

residue.

Types:

1. Initiator Caspases - cleave other procaspases

2. Execution Caspases - cleave other cellular

proteins involved in maintaining cellular integrity


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Intracellular signalsOxidative damage from free radicals, Radiation, Virus infection, Nutrient deprivation,

Pro-apoptotic Factors

Damage to the mitochondrial membrane increasing permeability

Entry of Cytochrome C into the cytoplasm

Cytochrome C binds to Apaf-1 forming an apoptosome

Apoptosome activates procaspase-9 to caspase-9

Caspase-9 cleaves and activates caspase-3 and caspase-7.

This executioner caspases activate a cascade of proteolytic activity that leads to:

Chromatin condensation, DNA fragmentation, Protein cleavage, Membrane

permeability


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External Mechanism


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Apoptosis triggered by external signals: theextrinsic or death receptor pathway

Fas and the TNF receptor are integralmembrane proteins with their receptor domains

exposed at the surface of the cell

binding of the complementary deathactivator (FasL and TNF respectively) transmitsa signal to the cytoplasm that leads to

activation ofcaspase 8 caspase 8 initiates a cascade of caspase

activation leading to

phagocytosis of the cell or apoptosis.


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Example : When cytotoxic T cells recognizeor bind to their target,they produce

more FasL at their surface.This binds with the Fas on the surface of the

target cell leading to its death by apoptosis.


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Role of Apoptosis

Why should a cell commit suicide? There are two different reasons.

1. Programmed cell death is as needed for proper developmentas mitosis is.

Example: The resorption of the tadpole tail at the time of its metamorphosis

into a frog occurs by apoptosis.

The formation of the fingers and toes of the fetus requires theremoval, by apoptosis, of the tissue between them.

The sloughing off of the inner lining of the uterus (the endometrium)

at the start of menstruation occurs by apoptosis. The formation of the proper connections (synapses) between

neurons in the brain requires that surplus cells be eliminated byapoptosis


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Role of Apoptosis

In Embryogenesis The development and maintenance of multicellular

biological systems depends on a sophisticated

interplay between the cells forming the organism, itsometimes even seems to involve an altruisticbehavior of individual cells in favour of theorganisms as a whole. During development manycells are produced in excess which eventually

undergo programmed cell death and therebycontribute to sculpturing many organs and tissues[Meier, 2000]


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Role of Apoptosis

In Development and Differentiation of Tissues an integral part of both plant and metazoan

(multicellular animals) tissue development

does not resemble the sort of reaction that comes asa result of tissue damage due to accident orpathogenic infection (cell death by necrosis). swelling and bursting - hence spilling their possibly damaging

internal contents into extracellular space

apoptotic cells and their nuclei shrink, and oftenfragment. In this way, they can be efficientlyphagocytosed (and, as a consequence of this, theircomponents reused) by macrophages or byneighboring cells.


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Role of Apoptosis

2. Programmed cell death is needed todestroy cells that represent a threat to

the integrity of the organism.


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Role of Apoptosis

Apoptosis and AIDS

hallmark- the decline in the number of the

patient's CD4+ T cells (normally about 1000per microliter (l) of blood)

responsible, directly or indirectly (as helper

cells), for all immune responses


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In Cancer

Virus associated cancer

Several human papilloma viruses(HPV) have beenimplicated in causing cervical cancer. One of them

produces a protein (E6) that binds and inactivates the

apoptosis promoterp53.

Epstein-Barr Virus (EBV), the cause of mononucleosisand associated with some lymphomas

produces a protein similar to Bcl-2

produces another protein that causes the cell to

increase its own production of Bcl-2. Both these

actions make the cell more resistant to apoptosis

(thus enabling a cancer cell to continue to proliferate).
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/TumorSuppressorGenes.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/TumorSuppressorGenes.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/B/BurkittLymphoma.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/B/BurkittLymphoma.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/TumorSuppressorGenes.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/TumorSuppressorGenes.html


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Some B-cell leukemias and lymphomas express highlevels ofBcl-2, thus blocking apoptotic signals they mayreceive. The high levels result from a translocation of the

BCL-2gene into an enhancer region for antibodyproduction.

Melanoma (the most dangerous type of skin cancer)cells avoid apoptosis by inhibiting the expression of the

gene encoding Apaf-1. Other cancer cells express high levels ofFasL, and can

kill any cytotoxic T cells (CTL) that try to kill them

because CTL also express Fas (but are protected from

their own FasL). Some cancer cells, especially lung and colon cancer

cells, secrete elevated levels of a soluble "decoy"

molecule that binds to FasL, plugging it up so it cannot

bind Fas. Thus, cytotoxic T cells (CTL) cannot kill thecancer cells


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In Immune system

The immune response to a foreign invader involves the

proliferation of lymphocytes T and/or B cells. When their

job is done, they must be removed leaving only a small

population of memory cells. This is done by apoptosis.

Very rarely humans are encountered with genetic defects inapoptosis. The most common one is a mutation in the gene

for Fas, but mutations in the gene for FasL or even one of

the caspases are occasionally seen. In all cases, the

genetic problem produces autoimmunelymphoproliferative syndrome or ALPS.


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Features: an accumulation of lymphocytes in the lymph nodes

and spleen greatly enlarging them.

the appearance of clones that are autoreactive; that is, attack"self" components producing such autoimmune disorders as

- hemolytic anemia

- thrombocytopenia

the appearance oflymphoma a cancerous clone oflymphocytes.


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Determination of cells undergoing

apoptosis

http://www.pnas.org/content/94/19/10385/F2.large.jpg


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I. Cytomorphological alterations

II. DNA fragmentation and micronuclei formation

III.Externalization of membrane

Phosphatidylserine

IV.Activation and presence of caspases,

cleaved substrates regulators and inhibitors


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Externalization of

Phosphatidylserine of the inner cell

membrane Cells that undergo PCD display an eat

me signals to elicit phagocytosis

The signal is Phosphatidylserine (PS) ofthe inner leaflet of the cell membrane

Apoptotic cell flips the PS to the outside

leaflet to let the phagocytic scavengersrecognize the signal


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This signaling of dying cells let the

scavenger cells phagocytose without

eliciting any inflammatory response

The lack of this PS receptors can lead to

the accumulation of undigested cells thathave undergone apoptosis


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DNA fragmentation & micronuclei

formation

Fragmentation of the chromatin result in

degradation of the nucleus and theformation of nuclear blebbing

Nucleic acid staining by the use of

fluorescent dyes can reveal micronucleibodies that are inherent to apoptotic cells


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Nuclear fragmentation and

micronuclei formation

http://physiologyonline.physiology.org/content/19/3/124/F2.large.jpg http://www.cancerquest.org/images/apo

ptosis.gif


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DNAfragmentation

Chromatin materials

condensed and

show a ladder

pattern of lowmolecular weight

DNA fragments

when

electrophoresis

technique is used.


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Cytomorphological alterations

Cytoskeleton degradation and asymmetry

of the cell membrane

Change in the permeability of the cell

membrane


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Degradation of cytoskeleton

Caspases digest the cytoskeletal proteins

of the apoptotic cells

This leads to the asymmetry of the cellmembrane


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Change in membrane

permeabilityApoptotic cells have different membrane

permeability than normal cells

Determination of possible apoptotic cells isthrough the use of stains (can either be

fluorescent or not) that take advantage of

this change in permeability Stains able to label the apoptosome with

the dye


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Detection and presence of

Caspase Caspase are cysteine-aspartic acid

specific proteases that mediates the

events that are associated withprogrammed cell death

Caspase-3 key effector in the apoptosis pathway, amplifying the signal

from initiator caspases and signifying full commitment to

cellular disassembly

Caspase-8 acts as an initiator of the caspase activation cascade

Apoptosis and Cell Necrosis

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