Apoptosis is a tightly regulated form of programmed cell death that involves the activation of caspases. There are intrinsic and extrinsic pathways of apoptosis. The intrinsic pathway involves signals within the cell such as DNA damage, causing mitochondrial membrane permeabilization and cytochrome c release. This forms the apoptosome and activates caspase-9 and caspase-3. The extrinsic pathway involves death receptors and activates caspase-8. Caspases cleave cellular proteins leading to cell death. Phagocytes then engulf and degrade the apoptotic bodies. Other forms of regulated cell death include necroptosis, pyroptosis and ferroptosis.

1. APOPTOSIS
Dr. Keerthika
SHORT TOPIC:

2. DEFINITION
Apoptosis is a type of cell death that is induced by a tightly
regulated suicide program in which cells destined to die
activate intrinsic enzymes that degrade the cells’ genomic
DNA and nuclear and cytoplasmic proteins.
PROGRAMMED CELL DEATH

3. ETYMOLOGY
APOPTOSIS: IN GREEK - FALLING OFF of leaves from a tree.
HIPPOCRATES- used the term to mean FALLING OFF THE BONES
GALEN- extended the term to mean DROPPING OF THE SCABS
James CORMACK- reintroduced the term for medical use after two decades
Pronunciation debate between second P being silenced or pronounced, John kerr
in his paper thanked comrack and mentioned the second of p is silent like in ptosis
and the stress should be given in the penultimate word.

4. DISCOVERIES
1842- German scientist CARL VOGT - principle of apoptosis
1885- Anatomist WALTHER FLEMMING -precise the process of programmed cell
death
1965- JOHN KERR was able to distinguish apoptosis from traumatic cell death.
JOHN KEER received the PAUL EHRLICH AND LUDWIG DARMSTAEDTER PRIZE
ON MARCH 14, 2000, shared with Biologist H.ROBERT HORVITZ
2002- NOBEL PRIZE IN MEDICINE was awarded to SYDNEY BRENNER, H.ROBERT
HORVITZ and JOHN SULSTON for their work identifying GENES THAT CONTROL
APOPTOSIS in nematode c.elegans and homologous of these genes function in
humans to regulate apoptosis.

5. APOPTOSIS
CAUSES
PHYSIOLOGICAL PATHOLOGICAL

6. ● Death by apoptosis is a normal phenomenon that serves to
eliminate cells that are no longer needed, or as a
mechanism to maintain a constant number of various cell
populations in tissues.
● Cells undergo apoptosis because they are deprived of
necessary survival signals,
● or they receive pro-apoptotic signals from other cells
● And they are removed by phagocytosis
PHYSIOLOGICAL CAUSES

7. The removal of supernumerary cells during development:

8. Involution of hormone-dependent tissues on hormone withdrawal

9. Cell turnover in proliferating cell populations-HOMEOSTASIS

10. Elimination of potentially harmful self-reactive LYMPHOCYTES

11. DDeath of host cells that have served their useful purpose

12. PATHOLOGICAL CAUSES
Apoptosis eliminates cells that are injured beyond repair
without eliciting a host reaction, thus limiting collateral tissue damage.
Death by apoptosis is responsible for loss of cells in a variety of
pathologic states:

13. DNA damage.

14. Accumulation of misfolded proteins.

15. Cytotoxic T Lymphocytes-mediated mechanism
apoptosis of infected cells in an attempt to eliminate reservoirs of infection.

16. Pathologic atrophy in parenchymal organs

17. Morphologic and Biochemical
Changes in Apoptosis

19. Cell shrinkage
● Cell size reduced
● Cytoplasm dense and
eosinophilic
● Organelles : relatively normal are
more tightly packed.

20. Chromatin condensation
● MOST CHARACTERISTIC
FEATURE OF APOPTOSIS
● Chromatin aggregates
peripherally, under nuclear
membrane

21. Cytoplasmic blebs and Apoptotic bodies
● Extensive surface membrane
blebbing

22. Nuclear Fragmentation
● Fragmentation of death cells into
membrane bound apoptotic
bodies

23. Phagocytosis
Apoptotic bodies are rapidly ingested by phagocytes and degraded by the
phagocyte’s lysosomal enzymes.

24. MECHANISM OF APOPTOSIS

25. APOPTOSIS results from the activation of enzymes called CASPASES
CASPASES
● Protases
● Containing a Cysteine in their active site
● Cleave proteins after Aspartic residues
Presence of activated caspase is the marker for apoptosis

26. Process of Apoptosis
1.Initiation phase :
Some caspases become catalytically
active and unleash a cascade of
other caspases
2.Execution phase :
Terminal caspases trigger cellular
fragmentation
Regulation of these enzymes depends on a finely tuned balance b/w
the abundance and activity of apoptotic and anti-apoptotic proteins.

27. -CYTOCHROME C
-PRO APOPTOTIC CELLS

28. EXTRINSIC PATHWAY
INITIATED BY ENGAGEMENT OF PLASMA MEMBRANE DEATH RECEPTORS
Death receptors:
TNF that contain a cytoplasmic domain involved in protein protein interaction.
Important in delivering apoptotic signalling
Some TNFr don’t have cytoplasmic death domains, their function is to activate inflammatory cascade
system.
Best known death receptor: TNFr1 and its related protein called Fas (CD 95). The ligand of Fas is
called Fas L (Fas Ligand).
FasL is expressed in T cells that recognise self antigens and on some CTLs that kill virus infected and
tumor cells.

29. DEATH INDUCING MOLECULE (FasL)
DEATH RECEPTORS (DEATH BUTTONS)-
TNF RECEPTOR
Fas associated death domain (FADD)
Autocatalytic caspase activation
INITIATOR CASPASE:
Procaspase 8 OR 10 (INACTIVE)
Caspase 8 OR 10 (ACTIVE)
EXECUTIONER CASPASE (CASPASE 3,6,7)
DNAase
APOPTOSIS

30. INTRINSIC PATHWAY
Responsible for apoptosis in most physiological and pathological
situations.
Increased permeability of the mitochondrial outer membrane with consequent
release of death inducing molecules from the mitochondrial intermembrane space
into cytoplasm.
Mitochondria is a double edged sword:
-produce energy that sustains cell viability
-when released into cytoplasm, initiates suicide program apoptosis

31. Bcl family
Release of pro-apoptotic proteins such as cytochrome C is determined by the
integrity of the outer mitochondrial membrane which is tightly controlled by bcl2
family of the proteins.
There are more than 20 members in the bcl family and they divided into three
groups based upon their pro or anti apoptotic effect
bcl 2 is commonly expressed gene.

32. Anti- apoptotic proteins:
Also known as pro-life
BCL2, BCLX and MCL1
Posses BH(1-4 domains)
Prevent cleavage of cytochrome C by
keeping the mitochondrial membrane
impermeable
Pro-apototic proteins:
Also known as Pro-death proteins
BAX, BAK
Posses BH(1-3 domains)
assumed , they form a channel in the
outer membrane that allows
cytochrome C leakage from
intramembranous space

33. Regulated apoptosis initators:
BAD, BIM, BID, PUMA, NOXA
One BH domain, the third of the four BH domain- BH3 only domain
Following cellular stress and damage, upregulated and activated they can initiate
apoptosis.

34. Growth factors and other survival signals
Antiapoptotic proteins such as BCL2
Prevent apoptosis

35. Cell injury
Activation of BH3 only proteins
Antagonize BCL2 and activates BAX
and BAK
Proteins from inner mitochondrial
membrane to cytoplasm
Cytochrome c + Apoptosis activating
factor -1,
Apoptosome
Activates capsases 9
Execution pathway
Apoptosis
Apoptosis inducing factors like Smac/
DIABLO
Neutralize physiological inhibitors of
apoptosis in cytoplasm

39. EXECUTION PHASE
THE INTRINSIC AND EXTRINSIC PATHWAYS COVERAGE TO ACTIVATE A
CASPASE CASCADE THAT MEDIATES THE FINAL PHASE OF APOPTOSIS
CASPASES 8 OR 10 AND CASPASES 9
CASPASES 3, 6.
DNASE

40. CASPASES:
PROTEOLYSES STRUCTURAL COMPONENT OF THE NUCLEI
PROMOTES FRAGMENTATION OF NUCLEI
DNAse
DNA degradation

41. REMOVAL OF DEAD CELLS
APOPTOTIC BODIES : BITE FRAGMENTS THAT EDIBLE FOR PHAGOCYTES
CHANGES PROMOTING THE PHAGOCYTOSIS:
-PHOSPHATIDYLSERINE FLIPS OUT, recognised by macrophages
-apoptotic cells secrete soluble factors that recruit phagocytes, leading to their engulfment.
-apoptotic bodies coated with natural antibodies and proteins of complement system like C1q
notably
Eat me signals provided by the apoptotic cell for the phagocytosis process is called efferocytosis

42. Efferocyotsis:
Efficient
Dead cells disappears within minutes without leaving a trace
Production of pro inflammatory cytokines is reduced

43. Necroptpsis
Pyroptosis
Ferroptosis
Other mechanism of cell death

44. Necroptosis
Programmed necrosis
Hybrid of both necrosis and apoptosis
Morphological and biochemically resemble necrosis -
loss of ATP,
swelling of cell and organelles ,
generation of ROS,
relapse of lysosomal enzymes ,
rupture of plasma membrane.

45. Mechanism of action
Caspases independent
Ligation of a receptor by ligand
TNF receptor can cause both apoptosis and necroptosis
Necroptosis involve RIPK1 and RIPK3 (receptor interacting protein kinase)
TNFR1 recruits multiprotein complex and RIPK3 phoshorylates a cytoplasmic
protein called MLKL,
Plasma membrane disruption: characteristic of necrosis

46. Causes of necroptosis
PHYSIOLOGICAL NECROPTOSIS:
Mammalian bone growth
PATHOLOGICAL NECROPTOSIS :
Cell death in ischemia-repressusion injury, neurodegerative disease such as
Parkinsonism disease
Necroptosis also acts as a backup mechanism in host defence against certain
viruses that encode caspase inhibitors. Eg: cytomegalovirus

48. Pyroptosis
Form of apoptosis that is accompanied by the release of the fever inducing
cytokines IL-1
Microbial products that enter infected cells are recognised by cytoplasmic innate
immune receptors and can activate multiprotein complex called inflamasome.
Activation of caspase -1, which cleaves IL-1 and release the biological active form
Caspase 4 & 5 also induce cell death.

50. Ferroproteins
Discovered in 2012
Cell death triggered when excessive intracellular levels of iron or reactive oxygen
species overwhelming the gulathione dependent antioxidant defences to cause a
unchecked membrane lipid peroxidation

51. Lipid peroxidation
Loss of plasma permeability
Cell death resembling necrosis
However regulated by specific signals unlike necrosis, can be prevented by
reducing iron levels.

53. Characteristic features:
Loss of mitochondrial Cristae
Ruptured outer mitochondrial membrane
Causes:
Linked to cell death in variety of human pathologies including cancer,
neurodegenerative disease and stroke.