1. Apoptosis
Dr Shoaib Raza

2. Apoptosis It is a pathway of cell death
Induced by tightly regulated suicide program
Activated enzyme that degrade cells’ own nuclear DNA, nuclear and cytoplasmic protein
Formation of apoptotic bodies that contain
Nuclear material and
Cytoplasmic organelles and material
No inflammatory response is elicited.

3. Physiologic examples of Apoptosis
Normal phenomenon that seems to eliminate the cells that are no longer needed
During embryogenesis, metamorphosis, etc
Involution of hormone dependent tissues after hormonal withdrawal
Cell loss in proliferating cell populations
Elimination of potentially harmful self reactive lymphocytes
Death of host cells that have subserved their useful purposes

4. Pathologic examples of Apoptosis
Eliminate cells that are injured beyond repair without eliciting a host reaction
DNA damage
Accumulation of misfolded protein
Cell death in certain infections (viral)
Viral factors (HIV)
Host factors (HBV)
Pathologic atrophy in parenchymal organs after duct obstruction

5. Morphology of Apoptosis
Cell shrinkage
Smaller size, dense cytoplasm, tightly packed organelles
Chromatin condensation
Peripheral aggregation of chromatin, breakup of nucleus
Apoptotic bodies formation
Phagocytosis by macrophages

8. Biochemical features of Apoptosis
Activation of caspases:
Caspases are proteolytic enzymes present in an inactive form in the cytoplasm
Cysteine proteases that cleaves aspartic acid residue (c asp ases)
Caspases are of two types
Initiator
Initiates and activates other caspases (8,9,10)
Executioner
Executes proteolysis and fragmentation of nucleus (3,6)

9. Biochemical features of Apoptosis
DNA & protein breakdown
Characteristic breakdown of DNA into large (50,000 – 3000,000) base pairs
Subsequent cleavage of DNA by Ca or Mg dependent endonuclease fragmentation into base pairs
Membrane alteration & phagocytosis
Membrane expresses more receptors for phagocytic cells
Phagocytosis is mainly by macrophages
No inflammatory response is elicited

10. Caspases Activation Activation of caspases may occur in two ways
Intrinsic (Mitochondrial) Pathway
Pro and anti apoptotic factors are usually present in cell
An imbalance would result in apoptosis
Bcl family of proteins are main regulators
Bcl-2, Bcl-x are main antiapoptotic factors
Bax/Bak channels are major proapoptotic mechanism
Release of Cytochrome-C and other proapoptotic proteins from mitochondria into cytoplasm
Cytochrome-C and Apaf-1 (apoptosis activating factor- 1) activates initiators

11. Extrinsic Pathway Is activated by
Engagement of plasma membrane death receptor
Fas binds with fasL
Fas associated death domain (FADD) activates
Procaspase-8 is converted into caspase-8
Initiator sequence begins

13. Execution Phase
Intrinsic or extrinsic pathway converge at the activation of execution pathway
Important Executioner caspases are caspase-3, caspase-6
They in turn activate DNAase
Break down of nuclear matrix
Proteolysis of cytoplasmic proteins

15. Example of Apoptosis Apoptosis after growth factor deprivation:
Endometrium, lymphocytes, neurons etc.
DNA damage-mediated apoptosis:
Radiation/chemotherapeutic agents induced apoptosis
Apoptosis by TNF family of receptors
Fas-FasL binding
CTL Mediated apoptosis:
Foreign antigen via perforin and granzyme B

16. Dysregulated Apoptosis
Too little or too much
Defective apoptosis (Increased survival)
Cancer (carcinogenesis)
Autoimmune disorders
Increased apoptosis (Excessive cell death)
Neurogenerative disorders
Infarction and stroke
Death of virus infected cell