apoptosis

3. Apoptosis
 Definition
 Causes / Significance
 Morphology
 Mechanism / Cellular events
 Clinical significance

4. Definition
1. Pathway of cell death induced by a tightly regulated
intracellular program in which cells destined to die,
activate enzymes that degrade the cells own nuclear
DNA & nuclear & cytoplasmic proteins.

5. Definition:
2. Internally programmed cell death.
3.“A form of cell death, designed to eliminate
unwanted host cells through activation of
coordinated, internally programmed series of
events effected by a dedicated set of gene
products”.

6. Causes/significance
PHYSIOLOGICAL
PATHOLOGICAL

7. PHYSIOLOGICAL SITUATIONS:
 Embryogenesis.
 Hormone dependent involution in adults.
 Cell deletion in proliferating populations.
 Cell death by cytotoxic T cells.
 Elimination of harmful self reactive lymphocytes.
 Death of host cells that have served their useful purpose.

8. PATHOLOGICAL CONDITIONS
 Injurious stimuli
 Cell injury in viral diseases
 Pathological atrophy in parenchymal organs after
duct obstruction
 Cell death in tumours

9. MORPHOLOGY
 Cell shrinkage
 Chromatin condensation
 Formation of cytoplasmic blebs & apoptotic
bodies
 Phagocytosis of Apoptotic cell by macrophages

10. HISTOLOGICAL EXAMINATION
 H&E STAIN
 Apoptotic cell appears as an round/oval mass of
intensely eosinophilic cytoplasm with dense
nuclear chromatin fragments.

11. MECHANISM/CELLULAR EVENTS
1. SIGNALING
2. CONTROL & INTEGRATION
3. EXECUTION
4. REMOVAL OF DEAD CELLS

12. 1. SIGNALING
 Transmembrane signals
-suppress preexisting death programs
-initiate a death cascade
 Tumour necrosis factor receptor (TNFR):
oligomerize leading to activation of initiator caspases & a
cascade of enzyme activation culminating in cell death.

13. 2. CONTROL & INTEGRATION
 Direct transmission of death signals by specific
adapter proteins to the execution mechanism.
 Regulation of mitochondrial permeability by
members of BCL-2 family of proteins.

14.  -mitochondrial permeability transition
 Cytochrome c – apoptotic trigger
 Cytochrome c binds to cytosolic proteins (e.g.,proapoptotic
protease activating factor/Apaf-1) & activates them triggering
execution caspases activation.
 BCL-2 suppresses apoptosis by preventing increased
mitochondrial permeability.

15.  Other members of BCL-2 family bind to BCL-2 &
modulate its antiapoptotic effect, thus BCL-Xl
inhibits apoptosis while BAX & BAD promote
programmed cell death.

16. 3. EXECUTION
 Protein cleavage
 DNA breakdown
 Protein cross-linking
 Phagocytic recognition

17. Protein cleavage
 Activation of caspases
-caspases – cleave cellular proteins (lamins) leads to break
up of nuclear scaffold & cytoskeleton
-activate DNase which degrade nuclear DNA.

18. DNA breakdown:
 DNA breakdown into oligonucleosomes in multiples of 180-300
base pairs by Ca2+ & Mg2+ dependent endonucleaes.
 DNA fragments identified by a technique agarose gel
electrophoresis.
 Apoptosis-regular fragmentation associated with activation of
p53 gene.
 Necrosis- “smeared” pattern.

19. Protein cross-linking
 Via transglutaminase activation
-converts soluble cytoplasmic proteins into
covalently condensed shell leading to formation
of apoptotic bodies.

20. 4. Phagocytic recognition
 Apoptotic cells express phosphatidyl serine in the outer
layers of plasma membrane ‘flipped’ from the inner layers.
 Some express thrombospondin an adhesive glycoprotein
 Other proteins secreted by phagocytes may bind to
apoptotic cells & opsonize the cells for phagocytosis.

21.  Tumours – apoptotic index as a measure of
proliferation
 Apoptosis in tumours increases following irradiation &
immune responses.
 Measurement of apoptosis in-vivo/ in-vitro following
treatment may predict effectiveness of therapy.
CLINICAL SIGNIFICANCE