A PRESENTATION ON CELL DEATH

1. CELL DEATH
PRESENTED BY :
SREYA. S
M. Pharmacy
I. Semester
Academic year:2019-2021
DEPARTMENT OF PHARMACOLOGY
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2. DEFINITION
 Cell death is the event of a biological cell ceasing to
carry out its functions.
 This may be the result of the natural process of old cells
dying and being replaced by new ones, or may result from
such factors as disease, localized injury, or the death of the
organism of which the cells are part.
 Cell death can occur in following ways-
1- Apoptosis (cell suicide)/ Autophagy
2- Necrosis (cell murder)
 Apoptosis or Type I cell-death, and autophagy or Type II
cell-death are both forms of programmed cell death,
while necrosis is a non-physiological process that occurs
as a result of infection or injury
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3. APOPTOSIS
• The cells of a multicellular organism are members of a highly
organized community. The number of cells in this community
is tightly regulated—not simply by controlling the rate of cell
division, but also by controlling the rate of cell death.
• If cells are no longer needed, they commit suicide by
activating an intracellular death program.
• This process is therefore called programmed cell death,
although it is more commonly called apoptosis.
• For an average human child between the ages of 8 to 14 years
old approximately 20 to 30 billion cells die per day
• Apoptosis is a highly regulated process. Apoptosis can be
initiated through one of two pathw.ays.
• In the intrinsic pathway the cell kills itself because it
senses cell stress, while in the extrinsic pathway the cell kills
itself because of signals from other cells
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4. APOPTOSIS: PATHWAYS
Apoptosis
Initiation
intrinsic extrinsic
Execution
caspases
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5. REGULATION
 There are a variety of factors responsible for regulating
apoptosis, both intracellular and extracellular. External signals
can include growth factors or specific signals from other cells,
whereas internal factors can include DNA damage or failure of
cell division.
Apoptosis Inducers Apoptosis Inhibitors
Withdrawal of growth
factors
Loss of matrix attachment
Glucocorticoids
Some viruses
Free radicals
Ionising radiation
DNA damage
Ligand binding at ‘death
receptors’
Presence of growth factors
Extracellular cell matrix
Sex steroids
Some viral proteins
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6. CASPASE ACTIVATION
 The mammalian initiator
caspase-9 is activated as a
complex with Apaf-1 and
cytochrome c in the
apoptosome. Caspase-9 then
cleaves and activates effector
caspases, such as caspase-3.
The effector caspases cleave
a variety of cell proteins,
including nuclear lamins,
cytoskeletal proteins, and an
inhibitor of DNase, leading
to death of the cell.
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7. THE INTRINSIC PATHWAY OF APOPTOSIS
 This pathway triggers apoptosis in response to internal
stimuli such as biochemical stress, DNA damage and lack
of growth factors.This pathway of apoptosis is the result of
increased mitochondrial permeability and release of pro-
apoptotic molecules (death inducers) into the cytoplasm
 The release of these mitochondrial proteins (mostly
cytochrome c) is controlled by a finely orchestrated
balance between pro- and anti-apoptotic members of the
Bcl family of proteins. This family is named after Bcl-2,
which was identified as an oncogene in a B-cell lymphoma
 Bcl2 family is classified in to 3 categories
 pro-apoptotic: promote apoptosis, inactive on normal
cell. Eg Bax, Bak
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8.  anti-apoptotic: inhibit apoptosis ,ensure cell survival -Bcl-2
Bcl-xl , Bcl-w
BH3-only proteins: only have a small BH3 domain . inhibit or
promote apoptosis eg; Bid, Bad, Bim, Puma, Noxa
 The pro-apoptotic molecules cause permeabilization of the
outer mitochondrial membrane, leading to efflux of cytochrome
c, which binds the adaptor Apaf-1 and the initiator caspase-9 in
the cytosol to form the apoptosome complex.
 This stimulates caspase-9, which in turn activates the effector
caspases.
 The mitochondrion also releases a protein called
Smac/DIABLO into the cytosol. Smac/DIABLO indirectly
promotes apoptosis by blocking the effects of a group of anti-
apoptotic proteins called inhibitor of apoptosis proteins (IAPs).
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9.  The anti-apoptotic proteins Bcl-2 and Bcl-XL inhibit
cytochrome c release, whereas Bax, Bak, and Bid, all pro-
apoptotic proteins, promote its release from mitochondria.
 Cytochrome c and deoxyadenosine triphosphate (dATP) bind to
APAF-1 to form a multimeric complex that recruits and
activates pro-caspase-9, an apoptosis-mediating executioner
protease that in turn activates the caspase cascade, resulting in
cell apoptosis.
 During this process, caspase-2, caspase-8, caspase-9 and
caspase-10 are involved in the initiation of apoptosis. Caspase-
3, caspase-6 and caspase-7 are involved in apoptosis. Caspase-
3 and caspase-7 regulate the inhibition of DNA repair and start
DNA degradation. In addition, caspase-6 regulates the
disintegration of the lamina and cytoskeleton.
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10.  Mitocondrial pathway
10
H2O2
casp9
Bcl2
PI3K
Akt
BAD
Apaf1
Cyt.C
ATP
casp3
casp3
IAPs
Smac/
DIABLO
AIF
Bax
Bax
p53
Fas
Casp8
Bid
Bid
Bid
DNA
damage

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12. THE EXTRINSIC PATHWAY OF APOPTOSIS
 Apoptosis is known as a physiological process of cell
deletion and is also a process of programmed cell
death, resulting in morphological change and DNA
fragmentation.
 It is stimulated by external or internal events of cells,
one of which is the extrinsic pathway mediated by the
death receptor.
 The death receptors include Fas receptors, tumor
necrosis factor (TNF) receptors, and TNF-related
apoptosis-inducing ligand (TRAIL) receptors.
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13.  As a surface receptor, for example, TNF receptor-1 (TNF-R1),
it will interact with TNF to induce the recruitment of adaptor
proteins such as Fas-associated protein with death domain
(FADD) and Tumor necrosis factor receptor type 1-associated
DEATH domain protein (TRADD), which recruits a series of
downstream factors, including Caspase-8, which is a critical
mediator of the extrinsic pathway, resulting eventually in cell
apoptosis.
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14.  The extrinsic pathway that initiates apoptosis is triggered by a
death ligand binding to a death receptor, such as TNF-α to
TNFR1
 The TNFR family is a large family consisting of 29
transmembrane receptor proteins, organized in homotrimers
and activated by binding of the respective ligand(s).
 They share similar cysteine-rich extracellular domains and
have a cytoplasmic domain of about 80 amino acids called the
"death domain" (DD).
 Besides TNFR1, the Fas and DR4/DR5 also involved the
pathway as death receptors and bind CD95 and TRAIL,
respectively.
 All of the ligand binding to receptors will lead, with the help of
the adapter proteins (FADD/ TRADD) to recruitment,
dimerization, and activation of a caspase cascade and
eventually cleavage of both cytoplasmic and nuclear substrates.14

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Receptor trimerization results in recruitment of several death
domains and eventually recruitment and activation of
caspase-8 and caspase-10. Active caspase-8 and caspase-10
then either initiate apoptosis

16. FLIP
 This pathway of apoptosis can be inhibited by protein
called FLIP
 binds to pro-caspase-8 but cannot cleave and activate the
caspase because it lacks a protease domain.
 Some viruses and normal cells produce FLIP and protect
themselves from Fas-mediated apoptosis.
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17. NECROSIS
 It is defined as focal death along with protein denaturation &
degradation of tissue by hydrolytic enzymes liberated by
cells. It is accompanied by inflammatory reaction
 Necrosis is caused by various agents such as hypoxia,
chemical and physical agents, microbial agents and
immunological injury
 Two essential changes bring about irreversible cell injury in
necrosis-cell digestion by lytic enzymes and denaturation of
proteins of proteins
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18. Types of Necrosis
 Cogulative necrosis
 Liquefactive necrosis
 Gangrenous necrosis
 Caseous necrosis
 Fat necrosis
 Fibrinoid necrosis
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19. COAGULATIVE NECROSIS
 This type of necrosis is caused by irreversible focal injury,
mostly from sudden cessation of blood flow(ischaemia) and
less often from bacterial and chemical agents
 A form of tissue necrosis in which the component cells are
dead but the basic tissue architecture is preserved for at least
several days.
 Presumably the injury denatures not only structural proteins but
also enzymes and so blocks the proteolysis of the dead cells; as
a result, eosinophilic, anucleate cells may persist for days or
weeks.
 the necrotic cells are removed by phagocytosis of the cellular
debris by infiltrating leukocytes and by digestion of the dead
cells by the action of lysosomal enzymes of the leukocytes.
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20.  Coagulative necrosis is characteristic of infarcts (areas
of ischemic necrosis) in all solid organs except the
brain.
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21. LIQUEFACTIVE NECROSIS
 This type of necrosis occurs commonly due to
ischaemic injury and bacterial or fungal infections
 It is seen in focal bacterial or, fungal infections,
because microbes stimulate the accumulation of
inflammatory cells and the enzymes of leukocytes
digest ("liquefy") the tissue in to a liquid viscous
mass
If the process was initiated by acute inflammation,
the material is frequently creamy yellow and is
called pus.
E.g.- hypoxic death of cells within the central
nervous system often evokes liquefactive necrosis.
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22. Gross Appearance: The tissue is in a liquid form and
sometimes creamy yellow because of pus formation.
Microscopic: Inflammatory cells with numerous
neutrophils.
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23. CASEOUS NECROSIS
 Caseous necrosis is encountered most often in foci of
tuberculous infection, caused by syphilis, certain fungi
 The term "caseous" (cheese-like) is derived from the friable
yellow-white appearance of the area of necrosis. On
microscopic examination, the necrotic focus appears as a
collection of fragmented or lysed cells with an amorphous
granular appearance.
 Caseous necrosis is often enclosed within a distinctive
inflammatory border; this appearance is characteristic of a
focus of inflammation known as a granuloma.

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24. FAT NECROSIS
 In fat necrosis the enzyme lipase release fatty acid from
triglycerides, then it form complex with calcium to form soaps
 This processed is usually triggered by several factors leading
to inflammation of the pancreas, otherwise known as
pancreatitis, can also occur in breast, salivary glands
 Causes of acute pancreatitis include alcohol, gall bladder
stones, poisoning, and insect bites. Since fat necrosis in the
pancreas is triggered by an inadvertent release of enzymes, this
process is also referred to as enzymatic fat necrosis.
 The trigger for necrosis in breast is usually trauma.
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25.  Gross Appearance: Whitish deposits as a result of the formation
of calcium soaps.
 Microscopic: Anucleated adipocytes with deposits of calcium
(Seen on H&E as areas of bluish stains)
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26. GANGRENOUS NECROSIS
 A type of tissue death caused by lack of blood supply or
infection , also associated with diabeties and long term
tobacco smoking
 Symptoms change in skin colour to red or black
 Types dry , wet , gas etc
 Dry gangrene is a form of coagulative necrosis that
develop in ischemic tissues ,also due to peripheral artery
disease
 Wet gangrene is characterised by thriving bacteria and
poor prognosis.It is infected by saprogenic
microorgasnism cause tissue to swell and emit bad smell.
 Gas gangrene due to bacteria,produce gas within tissue eg
clostridium
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27. FIBRINOID NECROSIS
 Fibrinoid necrosis is a pattern of cell death characterized
by endothelial damage and exudation of plasma proteins
 This pattern of necrosis is prominent when complexes of
antigens and antibodies are deposited in the walls of
arteries.
 Deposits of these "immune complexes," together with
fibrin that has leaked out of vessels, result in a bright pink
and amorphous appearance in H&E stains, called
"fibrinoid" (fibrin-like) by pathologists.
 The immunologically mediated diseases (e.g., polyarteritis
nodosa) in which this type of necrosis is seen.
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28.  Gross Appearance: Usually not grossly discernible.
 Microscopic: Deposition of fibrin within blood vessels.
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29. AUTOPHAGY
 The term ‘autophagy’, derived from the Greek meaning
‘eating of self’,
 It is the natural, regulated mechanism of the cell that
removes unnecessary or dysfunctional components.
 It allows the orderly degradation and recycling of cellular
components
 There are 3 types
 Macroautophagy
 Microautophagy
 Chaperone-mediated autophagy (CMA)
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30.  initial sequestered closes into a double membrane vesicle
the autophagosome
 some autophagosomes formed in a PI3P-enriched
(phosphatidylinositol 3-phosphate) membrane compartment
dynamically connected to the endoplasmic reticulum
 an autophagosome fuses with a lysosome
 Regulated process of the degradation and recycling of
organelles and cellular components
 Resulting in organelle turnover and in the bioenergetics of
starvation
 Could result in cell death
 through excessive self-digestion and degradation of
essential cellular constituents
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32. MACROAUTOPHAGY
 is the main pathway, used primarily to eradicate damaged
cell organelles or unused proteins.
 First the phagophore engulfs the material that needs to be
degraded, which forms a double membrane known as
an autophagosome , around the organelle marked for
destruction.
 The autophagosome then travels through the cytoplasm of
the cell to a lysosome, and the two organelles fuse .Within
the lysosome, the contents of the autophagosome are
degraded via acidic lysosomal hydrolase
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33. MICROAUTOPHAGY
 It is the direct uptake of soluble or particulate cellular
constituents into lysosomes.
 It translocates cytoplasmic substances into the lysosomes
for degradation via direct invagination, protrusion, or
septation of the lysosomal limiting membrane
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35. CHAPERONE-MEDIATED AUTOPHAGY
 It is a very complex and specific pathway, which involves the
recognition by the hsc70-containing complex.
 This means that a protein must contain the recognition site for
this hsc70 complex which will allow it to bind to this chaperone,
forming the CMA- substrate/chaperone complex.
 This complex then moves to the lysosomal membrane-bound
protein that will recognise and bind with the CMA receptor.
Upon recognition, the substrate protein gets unfolded and it is
translocated across the lysosome membrane with the assistance
of the lysosomal hsc70 chaperone.
 CMA is significantly different from other types of autophagy
because it translocates protein material in a one by one manner,
and it is extremely selective about what material crosses the
lysosomal barrier.
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36. REFERENCES
 Apoptosis an overview. www.sciencedirect.com. ScienceDirect Topics.
 Apoptosis." Reproductive and Cardiovascular Disease Research Group,
St. George's, University of London
 Renehen, Andrew G., Catherine Booth, Christopher S. Potten. "What is
apoptosis, and why is it important?" British Medical Journal
 Levine B, Kroemer G. Autophagy in the pathogenesis of disease. Cell
2008;132:27–42. [PubMed: 18191218]
 Mizushima N. Autophagy: process and function. Genes Dev
2007;21:2861–2873. [PubMed: 18006683]
 Molecular Biology of the Cell 4th ed. - IV. Internal Organization of the
Cell Chapter 17. The Cell Cycle and Programmed Cell Death
 "necrosis" Molecular Biology of the Cell -Cell- A molecular Approach
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