Apoptosis ppt
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APOPTOSIS Dr Vijay Marakala
APOPTOSIS
Mid nineteenth century (1951) Many observations indicated cell death plays a considerable role during physiological processes
In 1964 LOCKSHIN Programmed cell death
IN 1972 KERR FIRST INTRODUCED TERM APOPTOSIS WYLLEI IN A PUBLICATION CURRIE
APOPTOSIS
Apoptosis is an energy dependent programmed cell death for removal of unwanted individual cells
Definition
CELL DEATH
• Cells die by one of two mechanisms – necrosis or apoptosis
• Two physiologically different processes – Necrosis – death by injury – Apoptosis – death by suicide• Apoptosis and necrosis have different
characteristics
• Loss of membrane integrity
• Begins with swelling of cytoplasm and mitochondria
• Ends with total cell lysis, no vesicle formation, complete lysis
• Disintegration (swelling) of organelles
• Membrane blebbing, but no loss of integrity
• Begins with shrinking of cytoplasm and condensation of nucleus
• Ends with fragmentation of cell into smaller bodies
• Mitochondria become leaky due to pore formation involving proteins of the bcl-2 family.
• Loss of regulation of ion homeostasis
• No energy requirement• Random digestion of DNA
(smear of DNA after agarose gel electrophoresis)
• Postlytic DNA fragmentation (= late event of death)
• Tightly regulated process• Energy (ATP)-dependent • Non-random mono- and
oligonucleosomal length fragmentation of DNA(ladder type patern)
• Prelytic DNA fragmentation• Release of various factors into
cytoplasm by mitochondria• Activation of caspase cascade• Alterations in membrane
asymmetry
• Affects groups of contiguous cells
• Evoked by non-physiological disturbances (complement attack, lytic viruses, hypothermia, hypoxia, ischemia, metabolic poisons)
• Phagocytosis by macrophages • Significant inflammatory
response
• Affects individual cells • Induced by physiological
stimuli (lack of growth factors, changes in hormonal environment)
• Phagocytosis by adjacent cells or macrophages
• No inflammatory response
APOPTOSIS
Apoptosis in physiologic situations
Apoptosis in pathologic situations
Examples of apoptosis
APOPTOSIS
Apoptosis in physiologic situations
In the human body about 100,000 cells are produced every second by mitosis and a similar number die by apoptosis*
* Vaux and Korsmeyer, 1999,Cell
Formation of free and independe
nt digits
Development of the
brain
Development of
reproductive organs
Apoptosis in physiologic situations
Programmed cell death during embryogenesis
Apoptosis in physiologic situations
Cell loss in proliferaing cell
populations
Death of cells that have served their
useful purpose
Elimination of harmful self-reacttive
lymhocytes
Programmed cell death during adult stage
Apoptosis in pathologic situations
DNA damageAccumulation of mis-folded
proteins
Cell injury in certain
infections
Pathological atrophy in
parenchymal organs after
duct obstruction
Apoptosis eliminates cells that are genetically altered or injured beyond repair without eliciting a severe host reaction, thus keeping the damage as contained as possible.
Morphology of Apoptosis
CELL SHRINKAGE
CHROMATIC CONDENSATION
Biochemical features of Apoptosis
•By activation of caspases•Caspases activate DNAses
Protein Cleavage
•Cleavage into oligonucleosomes•By Ca2+-and Mg2+-dependent endonucleases
DNA Breakdown
•Phosphatidylserine •Thrombospondin
Phagocytic Recognition
Mechanisms of Apoptosis
The fundamental events in apoptosis is the activation of enzymes called CASPASES
Caspases are central initiators and executioners of apoptosis
Caspases
•Cysteine proteases•Cysteine-dependent ASPartate-specific proteASES
Mechanisms of Apoptosis
CASPASES
14 different members of the caspases-family have been described in mammals
Active cysteine residue in the catalytic site
Specificity in cleavage after an Asp residue
Synthesized as inactive zymogens (PROCASPASES)
DNA FRAGMENTATION AND GELELECTROPHORESIS
• Digestion of DNA starts after 2 hrs• 3&4 hrs after initiation of
apoptosis DNA is almost all degraded
• DNA is fragmented with restriction endonucleases
• Apoptosis induces 180 bp ladderingof DNA
DNA FRAGMENTATION - BIOCHEMICALHALLMARK OF APOPTOSIS
• DNA cleaved into non-random fragments• 180-200 bp fragments & multiples of this unit
Other morphological features ofapoptosis
Nuclearbreakdown(Hoechst)
CELLS ARE BALANCED BETWEEN LIFE AND DEATH
DAMAGE Physiological death signals
DEATH SIGNAL
PROAPOPTOTICPROTEINS
ANTIAPOPTOTICPROTEINS
Two distinct pathways converge on caspase acticvation
Mitochondrial pathway
• Intrinsic pathway
The death receptor pathway
• Extrinsic pathway
Mitochondria contain several proteinsthat are capable of inducing apoptosis
The choice between cell survival and death is determined by the permeability of mitochondria
The role of mitochondria in the induction of apoptosis
• Intrinsic pathway
Mitochondria
Cytochrome c release
Pro-caspase 9 cleavage
Pro-execution caspase (3) cleavage
Caspase (3) cleavage of cellular proteins,Nuclease activation,
Etc.
Death
BAXBAKBOKBCL-XsBADBIDB IKBIMNIP3BNIP3
BCL-2BCL-XLBCL-WMCL1BFL1DIVANR-13Several viral proteins
Mitochondrial pathway
The death receptor pathway
• Extrinsic pathway
Antiapoptotic Proapoptotic
Bcl-2 family members
A very large family with 30 members identified and belongs to both:
Bcl -2Bcl-XL
Bcl-W
A1Mcl-1
BaxBakBok
BidBimBikBadBmfHrk
NoxaPumaBlkBNIP3Spike
BH1, BH2,BH3,BH4
BH3
BH1, BH2,BH3
Physiological Intrinsicreceptor pathway damage pathway
MITOCHONDRIAL SIGNALS
Caspase cleavage cascade
Orderly cleavage of proteins and DNA
CROSSLINKING OF CELL CORPSES; ENGULFMENT(no inflammation)
APOPTOSIS
TOO MUCH: Tissue atrophy
TOO LITTLE: Hyperplasia
NeurodegenerationThin skin
CancerAthersclerosis
etc
APOPTOSIS
REFERENCES
Robin’s pathology
• 7th and 8th Edition
Introduction to apoptosis
• By Andreas Gewies ApoReview in2003