Pyroptosis

Slide 1 · PYROPTOSIS

Regulated, inflammatory lytic cell death

Canonical

GSDMD pores

Noncanonical

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · What defines pyroptosis?

Regulated initiation

Caspases mediate an intracellular death pathway.

Lytic execution

Gasdermin D pores culminate in membrane rupture.

Inflammatory output

IL-1β and other mediators are released.

Slide 3 · One process, two linked outcomes

Caspase-dependent GSDMD activation

Cell death

Membrane pores → osmotic disturbance → rupture

Inflammation

IL-1β and other mediators reach extracellular tissue

Slide 4 · Why “fiery death”?

The prefix pyro refers to fever.

A characteristic inflammatory output is interleukin-1β (IL-1β).

The defining event is lytic cell death coupled to inflammatory mediator release.

Name describes the inflammatory phenotype—not a separate source of heat.

Slide 5 · The microbial-infection context

Microbial material enters an infected cell

Intracellular sensing engages a pyroptotic route

Gasdermin pores develop

Infected cell dies and local inflammation follows

Slide 6 · Physiologic defense and pathologic excess

Potential host defense

Responds to intracellular microbial products

Eliminates an infected cell by lysis

Alerts adjacent tissue by mediator release

When exaggerated

Inflammatory injury may become excessive

Textbook links excess to sepsis

Autoimmune inflammatory disease is another association

Slide 7 · The regulated-cell-death landscape

Feature

Apoptosis

Necroptosis

Pyroptosis

Membrane fate

Usually preserved before clearance

Disrupted

Pore formation → rupture

Core machinery

Apoptotic caspases

RIPK1/RIPK3–MLKL

Inflammatory caspases–GSDMD

Typical reaction

Limited inflammation

Inflammatory lysis

Inflammatory lysis + cytokine release

Slide 8 · Pyroptosis is not ordinary apoptosis

Apoptosis

Cell shrinkage and chromatin condensation

Apoptotic bodies are rapidly cleared

Limited release of proinflammatory contents

Pyroptosis

Membrane-perforating GSDMD oligomers

Osmotic disturbance and cell rupture

Inflammatory mediator release

Slide 9 · Pyroptosis is not necroptosis

Mechanistic step

Necroptosis

Pyroptosis

Trigger context

TNFR1 or viral signals

Microbial sensing / cytosolic LPS

Activation arm

RIPK1–RIPK3

Caspase-1 or caspases-4/5

Membrane effector

MLKL

Gasdermin D

Shared result

Loss of membrane integrity

Loss of membrane integrity

Slide 10 · Pyroptosis is not ferroptosis

Ferroptosis

Iron-associated lipid peroxidation

Failure of antioxidant defenses

Membrane lipid injury dominates

Pyroptosis

Caspase-dependent GSDMD cleavage

Oligomeric protein pores

Inflammatory mediator escape

Slide 11 · The decisive questions

Recognition

What intracellular danger is detected?

Activation

Which caspase becomes active?

Execution

How does GSDMD form pores?

Outcome

How does membrane injury produce inflammation?

Slide 12 · Two pathways, one membrane effector

Canonical

Inflammasome → caspase-1

Noncanonical

Cytosolic LPS → caspases-4/5

GSDMD cleavage

Oligomers → pores → lysis

Slide 13 · Pattern-recognition receptors: The upstream logic

Innate immunity recognizes conserved microbial structures (PAMPs).

Injured and necrotic cells supply danger-associated signals (DAMPs).

Receptors occupy membrane, endosomal and cytosolic compartments.

Intracellular location helps determine which danger-sensing pathways can engage.

Slide 14 · PAMPs and DAMPs are not synonymous

PAMP

Pathogen-associated molecular pattern

Derived from microbes

Signals invasion or microbial presence

DAMP

Damage-associated molecular pattern

Arises from injured or dying host cells

Signals cellular damage

Slide 15 · Why cytosolic recognition matters

Intracellular microbial products

Cytosolic innate immune receptors

Inflammasome activation (canonical route)

Caspase-1 → gasdermin pores

Slide 16 · NOD-like receptors and the inflammasome

NOD-like receptors (NLRs) are one family of cytosolic sensors.

They detect microbial products and several signals of damage.

Some NLRs activate a multiprotein inflammasome.

The inflammasome activates caspase-1.

Slide 17 · Signals recognized by NLRs

Microbial products

Foreign molecules in the cytosol

Damaged-cell ATP

Extracellular/injury-associated signal

Uric acid

Damage-associated substance

Reduced intracellular K⁺

Ionic perturbation associated with danger

Slide 18 · Inflammasome: Functional architecture

Cytosolic sensor (e.g., NLRP3)

Adaptor component

Caspase-1 recruitment / activation

Maturation of IL-1β and GSDMD cleavage

Slide 19 · The three inflammasome modules

Sensor

Recognizes danger-associated signals

Adaptor

Supports multiprotein assembly

Caspase-1

Protease activated within the assembled complex

Slide 20 · Caspase-1 is an inflammatory protease

Activated caspase-1

Cytokine processing

Pro-IL-1β → mature IL-1β

Membrane execution

Gasdermin D cleavage → pore formation

Slide 21 · Precursor and mature IL-1β have distinct roles

Pro-IL-1β precursor

Caspase-1-mediated proteolytic cleavage

Biologically active IL-1β

Inflammatory signaling in surrounding tissue

Slide 22 · IL-1 synthesis ≠ IL-1 maturation

Production of precursor

Innate receptor stimulation induces IL-1 synthesis

Builds a precursor cytokine pool

Does not itself establish mature IL-1 activity

Proteolytic maturation

Inflammasome activates caspase-1

Caspase-1 processes the IL-1 precursor

Active cytokine can participate in inflammation

Slide 23 · Canonical pyroptosis: Pathway map

Microbial products sensed by cytosolic innate receptors

Inflammasome activation

Caspase-1 activation

GSDMD cleavage and IL-1β processing

Membrane pores, inflammatory mediator release, lysis

Slide 24 · Canonical initiation occurs inside the cell

Microbial products enter infected cells.

Cytoplasmic innate immune receptors recognize these products.

Inflammasome formation links sensing to an active protease.

Canonical does not simply mean every extracellular bacterial stimulus.

Slide 25 · Canonical pathway: Assembly before execution

Danger recognized

Inflammasome assembles

Caspase-1 becomes active

GSDMD acquires pore-forming activity

Slide 26 · Canonical pathway produces two outputs

Inflammasome-activated caspase-1

Mature cytokine

Proteolysis of pro-IL-1β

Death machinery

Proteolysis of gasdermin D

Slide 27 · Canonical cytokine arm

Inactive IL-1β precursor

Caspase-1 cleavage

Mature IL-1β

Mediator release through pyroptotic membrane injury

Fever and leukocyte recruitment

Slide 28 · Canonical membrane-injury arm

Caspase-1 active

GSDMD cleaved

GSDMD oligomerizes

Plasma membrane becomes porous

Osmotic imbalance → lytic death

Slide 29 · Canonical case: Interpret the cascade

An infected cell detects a microbial product in its cytoplasm. A multiprotein inflammasome becomes active.

Which protease and membrane effector are expected?

Caspase-1; Cleavage and oligomerization of GSDMD.

The inflammasome engages caspase-1, which processes both IL-1β precursor and GSDMD.

Slide 30 · Noncanonical pyroptosis: Defining trigger

The textbook specifies intracellular lipopolysaccharide (LPS).

LPS is produced by gram-negative bacteria.

This route activates caspases-4 and -5.

These caspases cleave GSDMD.

Slide 31 · Intracellular LPS as a danger signal

Gram-negative bacterial LPS

LPS present in the cytosolic compartment

Caspases-4/5 are activated

Gasdermin D is cleaved

Slide 32 · Noncanonical activation bypasses the first canonical step

Canonical entry

Innate cytosolic receptor sensing

Multiprotein inflammasome

Caspase-1 activation

Noncanonical entry

Intracellular gram-negative LPS

Caspases-4/5 activation

Direct convergence on GSDMD cleavage

Slide 33 · Noncanonical effector sequence

Intracellular LPS

Caspase-4 or caspase-5

Gasdermin D proteolysis

GSDMD oligomeric pores

Membrane disruption and lysis

Slide 34 · Do not confuse cytokine processing with pore activation

Mature IL-1β

Caspase-1 processes pro-IL-1β

The textbook makes this explicit for canonical activation

GSDMD activation

Either caspase-1 or caspases-4/5 can cleave GSDMD

Both branches create the membrane pore-forming effector

Slide 35 · Canonical vs noncanonical: Exact distinctions

Step

Canonical route

Noncanonical route

Input

Cytosolic microbial products

Cytosolic gram-negative LPS

Activation

Inflammasome

Caspases-4/5

Initiator protease

Caspase-1

Caspases-4/5

Common effector

GSDMD

GSDMD

Slide 36 · Pathway convergence is the central idea

Caspase-1

Inflammasome-dependent activation

Caspases-4/5

Intracellular LPS-dependent activation

GSDMD

Pore formation → lytic cell death

Slide 37 · Gasdermins are membrane pore-forming proteins

Gasdermins are the effector family named.

Gasdermin D (GSDMD) is the best-characterized example.

Proteolytic cleavage enables its pore-forming activity.

The effector is a membrane protein pore, not an enzyme that digests the entire membrane.

Slide 38 · GSDMD cleavage is the commitment step

Inactive/intact GSDMD

Inflammatory caspase cleavage

Activated pore-forming GSDMD component

Multimerization and membrane insertion

Slide 39 · Oligomerization creates an effective pore

Cleaved units

Individual activated GSDMD components

Oligomer

Multiple subunits assemble

Membrane pore

A conductive opening is formed in plasma membrane

Slide 40 · Plasma-membrane pores: Structural logic

Before cleavage

After GSDMD oligomerization

Pore-mediated flux

Schematic: Pore-forming proteins interrupt the barrier function of the plasma membrane.

Slide 41 · A pore changes permeability before rupture

GSDMD pore in plasma membrane

Disruption of normal membrane barrier

Altered ion/water distribution

Osmotic disturbance

Membrane rupture

Slide 42 · Mediator release and lysis are coupled

GSDMD pore formation

Release

IL-1β and other inflammatory mediators leave the cell

Physical failure

Local osmotic gradients become unstable → rupture

Slide 43 · Pyroptotic bodies appear before terminal rupture

GSDMD pores form

Osmotic potential becomes disturbed

Pyroptotic bodies develop

Plasma membrane eventually ruptures

Slide 44 · The terminal event is lytic cell death

Membrane integrity ultimately fails.

Cellular components escape into extracellular space.

The tissue is exposed to inflammatory mediators.

The process is regulated upstream despite the necrosis-like endpoint.

Slide 45 · Follow the entire injury sequence

Signal recognition

Caspase activation

GSDMD cleavage

Pore oligomerization

Mediator release + osmotic failure

Rupture and local inflammation

Slide 46 · How IL-1β produces local inflammation

Mature IL-1β is released

Endothelial activation and leukocyte adhesion

Recruitment of leukocytes

Inflammatory response in local tissue

Slide 47 · The link between IL-1β and fever

IL-1 is a fever-inducing proinflammatory cytokine.

Caspase-1 maturation enables biologically active IL-1β.

Lytic permeability permits release from the pyroptotic cell.

Fever reflects systemic inflammatory signaling, not cellular heat production.

Slide 48 · Why local inflammation amplifies tissue effects

Pyroptotic inflammatory mediators

Leukocyte recruitment

IL-1 supports a coordinated inflammatory infiltrate

Tissue consequences

Inflammatory response may protect but also injure tissue

Slide 49 · When host defense becomes pathogenic

Useful response

Recognize intracellular microbes

Remove infected cells

Recruit inflammatory defenses

Excessive response

Lytic death can extend injury

Released mediators amplify inflammation

Sepsis is a textbook-associated disorder

Slide 50 · Sepsis: Relevance without overclaiming

Excessive pyroptosis may contribute to sepsis.

The statement is contributory, not a claim that all sepsis is pyroptosis.

Gasdermin-mediated lysis provides a plausible inflammatory amplification route.

Do not substitute this mechanism for the broader multifactorial pathogenesis of sepsis.

Slide 51 · Autoimmune disease: An association, not a criterion

Autoimmune disease among conditions linked to excessive pyroptosis.

This does not establish that GSDMD activation diagnoses autoimmune disease.

Mechanistic association and validated clinical biomarker are different claims.

Slide 52 · Morphology: What the supplied passage supports

Explicitly described

Membrane pores and osmotic disruption

Formation of pyroptotic bodies

Eventually plasma-membrane rupture

Not established by this excerpt

Unique diagnostic H&E pattern

Specific organ-level gross morphology

Validated histologic cutoff or test threshold

Slide 53 · Apoptosis and pyroptosis: Fate of cell contents

Event

Apoptosis

Pyroptosis

Cell outline

Shrinks; apoptotic bodies form

Osmotic injury; pyroptotic bodies

Membrane integrity

Usually retained until clearance

Perforated; finally ruptures

Contents

Phagocytic clearance

Inflammatory mediator release

Inflammation

Usually limited

Intrinsic to the process

Slide 54 · Necroptosis and pyroptosis: Different pores

Feature

Necroptosis

Pyroptosis

Signaling

RIPK1/RIPK3 kinases

Inflammatory caspases

Effector

Phosphorylated MLKL

Proteolytically cleaved GSDMD

Final membrane event

Membrane disruption

Protein pore formation → rupture

Inflammatory result

Cell contents released

Cytokine + other mediator release

Slide 55 · Ferroptosis and pyroptosis: Different injury chemistry

Feature

Ferroptosis

Pyroptosis

Dominant trigger

Iron/ROS and impaired antioxidant defense

Microbial products / intracellular LPS

Effector change

Lipid peroxidation

GSDMD pore formation

Membrane defect

Peroxidized membrane lipids

Oligomeric membrane pores

Regulation

Iron-dependent pathway

Caspase-dependent pathway

Slide 56 · Integrated differential of lytic death

Necrosis

Uncontrolled injury → swelling/rupture

Necroptosis

RIPK1/RIPK3–MLKL → rupture

Pyroptosis

Caspase–GSDMD → rupture + IL-1β

Ferroptosis

Iron-linked lipid peroxidation → death

Slide 57 · Clinical application: Inflammasome route

A microbial product is sensed in an infected cell. Caspase-1 is activated, and mature IL-1β appears.

Which form of pyroptosis is represented?

Canonical pyroptosis.

Cytosolic sensing → inflammasome → caspase-1, with GSDMD downstream.

Slide 58 · Clinical application: Cytosolic LPS

Intracellular LPS from gram-negative bacteria activates caspases-4 and -5 in a model cell.

Which branch and effector are expected?

Noncanonical pathway; GSDMD activation.

The initiating caspases differ from canonical pyroptosis, but the pore effector is shared.

Slide 59 · Mechanistic application: Block GSDMD cleavage

A hypothetical intervention prevents inflammatory caspases from cleaving GSDMD, while upstream danger sensing remains intact.

What downstream event would the mechanistic model predict to be reduced?

GSDMD oligomeric pore formation and consequent membrane lysis.

Inference from the textbook causal pathway; This is not a claimed clinical treatment effect.

Slide 60 · Common conceptual errors

“Pyroptosis is the same as apoptosis.” — It is lytic and inflammatory.

“Every pathway uses caspase-1 first.” — Noncanonical initiation uses caspases-4/5.

“Caspases are the membrane pores.” — The pore-forming effector is GSDMD.

“IL-1β alone defines cell death.” — GSDMD-mediated lysis is central.

Slide 61 · Mechanism recap: Two entries, one exit

Canonical

Inflammasome → caspase-1

Noncanonical

Intracellular LPS → caspases-4/5

GSDMD membrane pores

Mediator release + osmotic failure → lytic death

Slide 62 · Essential teaching conclusions

Pyroptosis is regulated, pore-mediated, inflammatory lytic cell death.

Canonical activation links the inflammasome to caspase-1.

Noncanonical activation involves cytosolic LPS and caspases-4/5.

Both cleave GSDMD; Pore formation causes cytokine release and membrane rupture.

Excessive activation may contribute to sepsis and autoimmune inflammation.

Slide 63 · Principal textbook sources

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. (2026). Chapter 2: Other Mechanisms of Cell Death; “Pyroptosis,” p. 45.

Same textbook, Chapter 6: Cellular Receptors for Microbes and NOD-like Receptors and the Inflammasome.

Same textbook, Chapter 3: Recognition of Microbes and Damaged Cells; Tumor Necrosis Factor and Interleukin-1.