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APOPTOSISDr.Dinesh TJunior residentDepartment of
PhysiologyJIPMERsclero dinesh
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Discussion headingsIntroductionEtiopathogenesis Morphological,
Biochemical changesMechanism Intrinsic & Extrinsic
pathwayDisorders of apoptosisConclusion
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Introductionsclero dinesh
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Apoptosis - Definition
A pathway of cell death induced by a tightly regulated suicidal
program, in which the cells destined to die activate enzymes that
degrade cells own nuclear DNA and nuclear, cytoplasmic
proteins.
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Kerr Wyllie and Currie paper, British Journal of Cancer, 1972
Aug;26(4):239-57"We are most grateful to Professor James Cormack of
the Department of Greek, University of Aberdeen, for suggesting
this term. The word "apoptosis" () is used in Greek to describe the
"dropping off" or "falling off" of petals from flowers, or leaves
from trees. To show the derivation clearly, we propose that the
stress should be on the penultimate syllable, the second half of
the word being pronounced like "ptosis" (with the "p" silent),
which comes from the same root "to fall", and is already used to
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Historical aspects
German scientist Carl Vogt - Principle of apoptosis (1842).
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Walther Flemming Process of programmed cell death (1845).sclero
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John Foxton Ross Kerr Distinguish apoptosis from traumatic cell
death (1962).
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Nobel prize in 2002 Sydney Brenner , Horvitz, John Buston.
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Cell death mechanismsDeath by suicide Death by injurysclero
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APOPTOSISNECROSISNATURALYESNOEFFECTSBENEFICIAL
DETRIMENTALPhysiological or pathologicalAlways pathologicalSingle
cellsSheets of cellsEnergy dependentEnergy independentCell
shrinkageCell swellingMembrane integrity maintainedMembrane
integrity lost
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APOPTOSISNECROSISRole for mitochondria and cytochrome CNo role
for mitochondriaNo leak of lysosomal enzymesLeak of lysosomal
enzymesCharacteristic nuclear changesNuclei lostApoptotic bodies
formDo not formDNA cleavageNo DNA cleavageActivation of specific
proteasesNo activationRegulatable processNot
regulatedEvolutionarily conservedNot conservedDead cells ingested
by neighboring cellsDead cells ingested by neutrophils and
macrophages
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Significance of apoptosisDuring development many cells are
produced in excess which eventually undergo programmed cell death
and thereby contribute to sculpturing many organs and tissues
[Meier, 2000]In human body about one lakh cells are produced every
second by mitosis and a similar number die by apoptosis (Vaux and
Korsmayer ,1999, cell)Between 50 and 70 billion cells die each day
due to apoptosis in the average human adult. For an average child
between the ages of 8 and 14, approximately 20 billion to 30
billion cells die a day. ( Karam, Jose A. (2009). Apoptosis in
Carcinogenesis and Chemotherapy. Netherlands: Springer. ISBN
978-1-4020-9597-9)
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Etiopathogenesissclero dinesh
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Why should a cell commit suicide?
1. Programmed cell death is as needed for proper normal
development as mitosis is.
Examples: The resorption of the tadpole tail in frog .
The formation of the fingers and toes of the fetus requires the
removal, by apoptosis.
The sloughing off of the endometrium at the start of
menstruation.
The formation of the proper connections (synapses) between
neurons in the brain.
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2. Programmed cell death is needed to destroy cells that
represent a threat to the integrity of the organism.
Examples: Cells infected with viruses
Cells of the immune system
Cells with DNA damage
Cancer cells (Uncontrolled proliferated cells)
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Apoptosis in physiologic situations Programmed destruction
during embryogenesis
Involution of hormone dependent tissues
Cell loss in proliferating cell populations
Elimination of harmful self- reactive lymphocytes
Death of host cellssclero dinesh
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Apoptosis in bud formation during which many interdigital cells
die.They are stained black by a TUNEL method Incomplete
differentiation in two toes due to lack of apoptosissclero
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Apoptosis: in embryogenesisMorphogenesis (eliminates excess
cells):Selection (eliminates non-functional cells):sclero
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Apoptosis: in embryogenesisImmunity (eliminates dangerous
cells):Self antigenrecognizing cellOrgan size (eliminates excess
cells):sclero dinesh
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Apoptosis: importantance in adultsTissue remodeling (eliminates
cells no longer needed):Virgin mammary glandLate pregnancy,
lactationInvolution(non-pregnant, non-lactating)ApoptosisApoptosis-
TestosteroneProstate gland sclero dinesh
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Apoptosis: importantance in adultsTissue remodeling (eliminates
cells no longer needed):Resting lymphocytes+ antigen (e.g.
infection) - antigen (e.g. recovery) Apoptosissclero dinesh
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Apoptosis in pathological conditions - DNA damage
- Accumulation of misfolded proteins
- Cell death in certain infections
- Pathological atrophy in parenchymal organs
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Cells of the immune system CTLs induce apoptosis in each other
and even in themselves. Defects in the apoptotic machinery is
associated with autoimmune diseases such as lupus erythematosus and
rheumatoid arthritis.
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Cells infected with viruses One of the methods by which
cytotoxic T lymphocytes (CTLs) kill virus-infected cells is by
inducing apoptosis
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Cells with DNA damage Damage to its genome can cause a cell to
disrupt proper embryonic development leading to birth defects to
become cancerous.Cells respond to DNA damage by increasing their
production of p53. p53 is a potent inducer of apoptosis.
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Cancer cells Radiation and chemicals used in cancer therapy
induce apoptosis in some types of cancer cells.
Fig. 1: SC-1 induced apoptosis in stomach carcinoma cells Left:
Before induction Middle: 24h after induction Right: 48h after
inductionsclero dinesh
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Morphological & Biochemical changes
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Classic changes
Cell shrinkage Nuclear fragmentation Chromatin
condensationChromosomal DNA fragmentationFormation of cytoplasmic
blebs& apoptotic bodiesPhagocytosis
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HistologyApoptotic bodies Round oval mass of intensely
eosinophillic cytoplasmFragments of dense nuclear chromatin
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Bio chemical changes
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Mechanisms of apoptosis sclero dinesh
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Caspases Caspase are Cysteine- Aspartic acid specific proteases
that mediates the events that are associated with programmed cell
death.
Their catalytical activity depends on a critical
cysteine-residue within a highly conserved active-site pentapeptide
QACRG,
Caspases specifically cleave their substrates after Asp
residues. Caspase- 8, Caspase- 9acts as an initiator of the caspase
activation cascade.
Caspase-3key effector in the apoptosis pathway, amplifying the
signal from initiator caspases and signifying full commitment to
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InitiationAbsence of stimuli - hormones, growth
factorsActivation of receptors TNF familyHeat ,radiation,
chemicalsGenetically programmed events
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STAGES OF CLASSIC APOPTOSISHealthy cellDEATH SIGNAL / STIMULI
(extrinsic or intrinsic)Commitment to die (reversible)EXECUTION
(irreversible)Dead cell (condensed, crosslinked)ENGULFMENT
(macrophages, neighboring cells)DEGRADATIONsclero dinesh
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Receptor pathway (physiological):Death receptors:(FAS, TNF-R,
etc)FAS ligandTNFDeathdomainsAdaptor proteinsPro-caspase 8
(inactive)Caspase 8 (active)Pro-execution caspase
(inactive)Execution caspase (active)DeathMITOCHONDRIAsclero
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Apoptosis triggered by external signals: the extrinsic or death
receptor pathway
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Regulation of apoptosis
Regulatory proteins BCL -2, equivalent to CED -9 Apoptosis
depends on binding of BCL -2 with pro apoptotic and anti apoptotic
proteins.Situated in the outer mitochondrial membrane.Apaf -1
equivalent to CED -4. Tp 53, caspases, BAX, viruses such as adeno,
papilloma , hepatitis B.sclero dinesh
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Intrinsic pathway (damage):MitochondriaCytochrome c
releasePro-caspase 9 cleavagePro-execution caspase (3)
cleavageCaspase (3) cleavage of cellular proteins,nuclease
activation, etc. DeathBAXBAKBOKBCL-XsBADBIDB
IKBIMNIP3BNIP3BCL-2BCL-XLBCL-WMCL1BFL1DIVANR-13Several viral
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Intracellular signalsOxidative damage from free radicals,
Radiation, Virus infection, Nutrient deprivation, Pro-apoptotic
FactorsDamage to the mitochondrial membrane increasing
permeabilityEntry of Cytochrome C into the cytoplasmCytochrome C
binds to Apaf-1 forming an apoptosomeApoptosome activates
procaspase-9 to caspase-9Caspase-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 permeabilitysclero
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Physiological Intrinsicreceptor pathway damage pathway
MITOCHONDRIAL SIGNALSCaspase cleavage cascadeOrderly cleavage of
proteins and DNACROSSLINKING OF CELL CORPSES; ENGULFMENT(no
inflammation)sclero dinesh
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Steps sclero dinesh
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Disorders of apoptosissclero dinesh
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Apoptosis: Role in Disease TOO MUCH: Tissue atrophyTOO LITTLE:
HyperplasiaNeurodegenerationThin
skinetcCancerAthersclerosisetcsclero dinesh
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Apoptosis: Role in DiseaseNeurodegenerationNeurons are
post-mitotic (cannot replace themselves; neuronal stem cell
replacement is inefficient)
Neuronal death caused by loss of proper connections, loss of
proper growth
factors (e.g. NGF), and/or damage (especially oxidative
damage).
Neuronal dysfunction or damage results in loss of synapses or
loss of cell bodies (synaptosis, can be reversible; apopsosis,
irreversible)
PARKINSON'S DISEASE
ALZHEIMER'S DISEASE
HUNTINGTON'S DISEASE etc.sclero dinesh
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Apoptosis: Role in DiseaseCancerApoptosis eliminates damaged
cells (damage => mutations => cancer
Tumor suppressor p53 controls senescence and apoptosis responses
to damage.
Most cancer cells are defective in apoptotic response(damaged,
mutant cells survive)
High levels of anti-apoptotic proteins or Low levels of
pro-apoptotic proteins ===> CANCERsclero dinesh
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Apoptosis: Role in DiseaseCancerVirus associated cancerSeveral
human papilloma viruses (HPV) have been implicated in causing
cervical cancer. One of them produces a protein (E6) that binds and
inactivates the apoptosis promoter p53.
Epstein-Barr Virus (EBV), the cause of mononucleosis and
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).
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Some B-cell leukemia and lymphomas express high levels of Bcl-2,
thus blocking apoptotic signals they may receive. The high levels
result from a translocation of the BCL-2 gene into an enhancer
region for antibody production.
Melanoma (the most dangerous type of skin cancer) cells avoid
apoptosis by inhibiting the expression of the gene encoding
Apaf-1.
Apoptosis: Role in DiseaseCancersclero dinesh
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Other cancer cells express high levels of FasL, 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 the cancer cellsApoptosis: Role in
DiseaseCancersclero dinesh
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Apoptosis: Role in DiseaseAging
Aging --> both too much and too little apoptosis(evidence for
both)
Too much (accumulated oxidative damage?)---> tissue
degeneration
Too little (defective sensors, signals?---> dysfunctional
cells accumulatehyperplasia (precancerous lesions)sclero dinesh
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Apoptosis: Role in DiseaseApoptosis and AIDS Hallmark- the
decline in the number of the patient's CD4+ T cells (normally about
1000 per microliter (l) of blood).
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In Immune system
Very rarely humans are encountered with genetic defects in
apoptosis. The most common one is a mutation in the gene for
Fasmutations in the gene for FasL or even one of the caspases are
occasionally seen. Autoimmune lymphoproliferative syndrome or
ALPS.
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Cells are balanced between life and deathDAMAGEPhysiological
death signalsDEATH
SIGNALPROAPOPTOTICPROTEINS(dozens!)ANTIAPOPTOTICPROTEINS(dozens!)DEATHsclero
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Thank u.sclero dinesh
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