General Pathology - II

Cell

Death

Jaroslava Dušková

Inst. Pathol. ,1st Med. Faculty, Charles Univ. Prague

http://www1.lf1.cuni.cz/~jdusk/

Deathirreversible damage of the

morphological & functional integrity of

organism cells

Cell Death

apoptosis necrosis

Apoptosis induced (from outside) or genetically programmed cell

death

(cell execution / suicide)

logical and functional contrary to mitosis a system for the removal of unnecessary,

aged, or damaged cells

Necrosis

cell death caused from external insult

ApoptosisBiochemistry

– expression of genes de novo– production of apoptosis related proteins

inductors of the cell death p53, MTS1 - Multiple Tumor Suppressor, c-myc, Fas

inhibitors of the cell death bcl-2,

– activation of endonucleases– fragmentation of DNA – polymerisation of actin

• Triggered by a wide range of stimuli.

• Cell surface receptors like Fas or

tumor necrosis factor receptor 1 (TNFR1).

• Interplay of proapoptotic (Bax, Bad, Bid, Bik,

and Bim) and antiapoptotic (Bcl-2 and Bcl-XL)

proteins

Apoptosis -1

http://www.sigmaaldrich.com

Oxidative Damage -1

• Endogenous production of reactive oxygen by mitochondria.

• Increased permeability transition (PT) in the mitochondrial membrane

Oxidative damage -2

Apoptogenic factors leak into the cytoplasm

cytochrome c and apo - inducing factor (AIF) a cascade of proteolytic

activity DNA

fragmentation mutations cell death.

Mitochondria in ApoptosisOxidative damage - 3

Bcl-2 and Bcl-X –prevent pore formation

–block the release of cytochrome c from the mitochondria

– prevent activation of the caspase cascade and apoptosis.

Caspase Cascade -1

Caspases - a class of cysteine

proteases involved in apoptosis.

A proteolytic cascade activates

enzymes that subsequently

degrade cellular targets.

Caspase Cascade - 2

The mitochondrial stress pathway - release of cytochrome c from mitochondria

Granzyme B and perforin (proteins

released by cytotoxic T cells) induce apoptosis in target cells by forming transmembrane pores

Caspase Cascade - 3

Caspase-activated DNAse (CAD) may be activated through the cleavage of its associated inhibitor ICAD. CAD is then able to interact with components such as topoisomerase II (Topo II) to condense chromatin and lead to DNA fragmentation.

Granzyme B forming transmembrane pores cleavage of effector caspases such as

caspase-3 In addition, caspase-independent

mechanisms of granzyme B-mediated apoptosis have been suggested.

Caspase-activated DNAse (CAD) is activated through the cleavage of its associated inhibitor ICAD by caspase-3.

CAD interacts with topoisomerase II (Topo II) to condense chromatin– DNA fragmentation and ultimately

apoptosis.

Fas Signaling Pathway

Fas/APO-1/CD95 is a member of the tumor necrosis factor (TNF) receptor superfamily– mediator of apoptotic cell death, – involved in inflammation.

Binding of the Fas ligand (Fas-L) induces trimerization of Fas in the target cell membrane.

Activation of Fas causes the recruitment of Fas-associated protein with death domain (FADD)

activation of caspase-8. Activated caspase-8 cleaves (activates) nine

other pro-caspases a caspase cascade leads to apoptosis.

TNF Signaling Pathway -1 TNF receptor (TNFR)

transduces growth regulatory signals into the cell.

TNF is mitogenic for normal cells

TNF initiates apoptosis in transformed cells causing DNA fragmentation and cytolysis.

TNF Signaling Pathway - 2 The TNF-induced cell survival

pathway is mediated by the transcription factor NF-kB.

cells in which the NF-kB signaling pathway is blocked are more likely to undergo apoptosis in response to TNF.

The availability of NF-kB may play a critical role in the ability of TNF to act as an apoptosis-inducer and anti-tumor agent.

ATM/p53 Signaling Pathway

The ataxia telangiectasia-mutated gene (ATM) encodes a protein kinase that acts as a tumor suppressor.

ATM activation stimulates DNA repair and blocks cell cycle progression.

ATM-dependent phosphorylation of p53 p53 can cause growth arrest of the cell

at a checkpoint to allow for DNA damage repair or can cause the cell to undergo apoptosis if the damage cannot be repaired.

p53 is mutated in over 50% of all human cancers.

Integrin Signaling in Cell Survival and Death Integrins are heterodimeric

transmembrane receptors composed of a- and b-subunits.

Approximately 20 integrins have been identified

Focal adhesion kinase (FAK) is activated via autophosphorylation when cells interact through integrins.

Depending on the integrin interactions, the cell can either survive or undergo apoptosis.

Caspase Activation Intristic Pathway -1

Cytochrome c release from the mitochondria of pre-apoptotic cells

Binding to Apaf-1 in the presence of dATP/ATP.

Conformational change in Apaf-1 allowing the molecules of Apaf-1 to associate with each other.

Caspase Activation Intristic Pathway - 2

A wheel-like structure that contains 7 molecules each of Apaf-1, cytochrome c and ATP.

Pro-Caspase-9 autoactivation Mature caspase-9 remains bound

to the apoptosome

Activation of executioner caspases such as caspase-3 and caspase-7.

ApoptosisMorphology

– chromatin condensation

– cell shrinkage– budding and forming of apoptotic bodies

(emission of pseudopodia)

– karyorrhexis (not pathognomonic for apoptosis)

ApoptosisMeaning

physiological process necessary for right organ formatting and life course

pathological process leading to organism damage - e.g. atrophy

ApoptosisOntogenesis

intestinal mucose, genit. tract, immune system - T lymphocytes

Tissue & organ structures turnover intestinal mucose, blood, endometrium

Physiological involution neonatal adrenal cortex, thymus, breast after lactation period

Atrophy preassure, hyperplasia regression, slight ischemia

ApoptosisDetection

TUNEL = Terminal deoxynukleotidyl transferase-

mediated dUTP Nick End Labeling

silver methenamin impregnation

NecrosisBiochemistry

– no expression of genes de novo– energy dependent membrane

systems damaged hypoxia, toxins

– changes in concentrations of ions– increased water volume (oncosis)

– autolysis

NecrosisMorphology

– pyknosis, karyorhexis, karyolysis

– denaturation of proteins - eosinophilia

– cell swelling– cell budding (cytoplasmic protrusions)

NecrosisMeaning

pathological process

leading to a temporary

organism damage or death

Necrosis Classification according to the tissue macroscopy:

– simple– liquefaction– coagulation

+ special types: caseation, Zenker´s of waxy appearance

Necrosis - further development:

– no death of organism

– gangrene sicca humida emphysematosa (gas

g.)– demarcation, sequestration

regeneration repair

Necrosis - Causes:

chemical– chlorinated hydrocarbons, heavy metal

compounds, ethyl- alcohol, aphlatoxins, ... physical

– mechanical trauma, UV light, ionizing radiation, heat, cold, ….

biologic– bacteria, viruses, fungi...

Atrophy diminution of organ or tissue after full development has been attained (versus hypoplasia, aplasia) simple (x hypertrophy) numerical (x hyperplasia)

Atrophy - causes:

vascular pressure inactivity inanition neurogenic ionizing radiation

involution senile postinflammatory endocrine

unknown cause

Atrophy - meaning:

may be reversible loss of specialised structures

& hypofunctionclinically silent or unimportant

(involution)clinically apparent

metaplasia, increase of the supportive tissues - pseudohypertrophy