Apoptosis😊

• Programmed cell death.

• Caspase dependent.

• NO inflammation.
• Differentiates it from necrosis.

• Also induced by Glucocorticoids

• Physiological Example:
• Organogenesis or embryogenesis.
• E.g., removal of tissue between developing fingers.

• Pathological Examples

ㅤ	Councilman bodies	Civet bodies
Seen in	Hepatitis C virus	Lichen planus
ㅤ	Mnemonic: C for C	ㅤ

B. Mechanism of Apoptosis:

• Two main phases: 
• Initiation 
• execution.

1. Initiation

• Intrinsic → Mitochondria mediated
• Note: Caspase 9 → middle → internally
• UV light → BIM, BID, BAD, PUMA, NOXA → ↑ Pro apoptotic (P53, XS, BAK/BAX), ↓ Anti apoptotic (BCL XL, BCL 2, MCL 1) → Sent stress signal to mitochondria → Stimulate Mitochondria to produce Cytochrome C (along with Smack, Diablo) → Cytochrome C combine with APAF 1 → Form Apoptosome → Activate Procaspase 9 → Caspase 9

• Extrinsic → T cell mediated
• Note: Caspase 8 and 10 (on either sides → externally)
• CD 8 T Cell → CD 95 Ligand interact with → CD 95 receptor on cell surface → CD 95 tripolymerisation → Attract FADD (Fas-Associated Death Domain) → FADD convert Procaspase 8 and 10 → Caspase 8 and 10 (Inhibited by FLIP (anti-apoptotic molecule)
• Causes
• Virus
• Cancer

2. Execution

• Caspase 8, 9, 10 → Activate Procaspase 3, 6, 7 → Caspase 3, 6, 7 → Cell fragments into apoptotic bodies (Membrane bound, nucleus may or may not be present) → Flipping of PS (Phosphatidylserine occurs) → “Eat me Signal/Efferocytosis” → Macrophages phagocytosis

• Definition of CASPASE:
• C: cysteine residues.
• ASP: aspartic acid (enzyme breaks tissue after this acid).
• ASE: an enzyme.

1. Initiation Pathways:

Pro-apoptotic Molecules

• P-53

• BAX

• BCL-XS

• Mnemonic: Stab 53 () times → Xtra () small person in the back (BAX)

Anti-apoptotic Molecules

• BCL2

• MCL1

• BCL-XL

• Mnemonic: “LL” containing molecules “lower” apoptosis

2. Execution Phase:-

Microscopic Features and Markers of Apoptosis:

Microscopic Features:

• Cell shrinkage.

• Extremely pink cytoplasm.

• Extremely blue nucleus due to nuclear chromatin condensation.

• Hallmark of Apoptosis: 
• Nuclear chromatin condensation (Pyknosis)

• Membrane outline intact

Markers:

• Molecular Marker: 
• Annexin V
• Phosphatidyl serine flipping
• Mnemonic: Apoptosis = A"Penta" for Annexin V.
• (Note: Annexin A1 seen in hairy cell leukemia).
• TUNEL stain:
• Positive in apoptosis.
• Negative in necrosis.
• Mnemonic: Positive for apoptosis; Negative for necrosis.

• CD Marker: 
• CD95.

Gel Electrophoresis:

• Step-ladder pattern:
• Apoptosis >> necrosis
• Seen in both.

• Smearing pattern:
• Necrosis

• Mnemonic:
• Apoptosis → Paisa (ATP dep) koduth
• Hep C (Hep C) ulla Councilmane Plan (Lichen planus) conceive (civette) cheythu → Step by step aytt (Stepladder) Veti vetti (shrink) cheyth → Tunnelill (TUNEL) upekshichu

Comparison of Cell Death Pathways

Newer Cell Deaths

A. Necroptosis:

• Aka programmed necrosis.

• A combination of necrosis and apoptosis.

• Key definition:
• A caspase-independent programmed cell death.
• Caspases are never used in active form.

• Mechanism : Apoptosis (But mediated by TNF, RIP 1 & 3).

Occurrence:

• Physiological: 
• Growth plate formation.

• Pathological:
• Fatty liver (steatohepatitis).
• Acute pancreatitis
• Neurodegenerative diseases

Mechanism:

• Mnemonic: 1 2 3 death.
1. Binding of TNF (Tumor Necrosis Factor) with TNF receptor.
2. Formation of a trio:
• RIP kinase 1 (RIPK1).
• RIP kinase 3 (RIPK3).
• PRO-caspase 8 (not active caspase 8).
3. MLKL (Mixed Lineage Kinase domain-like protein) phosphorylation
• causing cell death.

• Mnemonic:
• Assassin → He was alcoholic → fatty liver and pancreatitis → but he had good growth (Growth plate) → He Thuni (TNF) RIP (RIP 1,3) cheyth 8il (Procaspase 8) ninn Milk (MLKL) kudichu
• He dont use condom (No caspase)

B. Pyroptosis:

• "Pyro" means fever

• Association:
• Salmonella and Shigella.

• Mechanism:
1. NOD2 receptors welcome and receive the bacteria.
2. Activation of inflammasomes.
3. Caspases involved: Caspase 1, 4, 5, 11.
4. Fever Connection:
• Caspase 1 activates Interleukin-1 (IL-1).
• IL-1 is known to cause fever.

• Important Distinction:
• Uses NOD receptors

• Mnemonic: pyro → fever → bacteria → bacteria says i love u (1, 4, 5 → 11 times) to cell → cell nods (NOD 2) and blushes (inflammasome)

C. Ferroptosis:

• Definition: Iron-induced cell death.

• Nature: Very similar to necrosis.

• Lipid peroxidation

• Mechanism:
• Fenton's reaction
• Iron → Form free radicals → Cell death

• Master Regulator: 
• GPX4 (Glutathione Peroxidase Type 4).
• Mnemonic: 4 → Ferro