Docstoc

Apoptosis and necrosis

Document Sample
Apoptosis and necrosis Powered By Docstoc
					CELL INJURY AND CELL DEATH


        NECROSIS
           and
        APOPTOSIS
               NECROSIS

Necrosis is the term for the passive
morphological changes that occur to
cells of a tissue following their death.

Necrosis results from the cessation of energy-dependent
processes that maintain metabolism of living organisms
                 APOPTOSIS

Apoptosis is an active gene-directed
mechanism of cell death. In normal
healthy tissues it is particularly associated
with maintenance of tissue architectural
integrity, and of sculpting in the embryo.

It is characteristic of a variety of diseases and is an important
mechanism in both tumour behaviour and anti-tumour therapy
NECROSIS
   Plan of the events contributing to necrosis




(Wyllie A. 1982, in ‘Cell Death in Biology and Pathology’, Bowen and Lockshin)
In necrosis, membrane damage results
in leakage between discrete cellular
compartments.

For example, lytic enzymes might escape
from lysosomes.

There is haphazard redistribution of ions
and electrolytes.
Cytoplasmic destructive changes include
organelle vacuolation, initial cell swelling
protein degradation, ultimate cell rupture.

Typical nuclear changes are loss of cohesion
of contents, karyorrhexis and karyolysis
Tissue architecture is lost.

Parenchymal and stromal
inter-relationships become
distorted.

Substantial aggregates of
dead material may accrete.
                                     Distorted p/s relationships




       Lost architecture



         Substantial aggregates of dead material




Periportal necrosis after paracetamol poisoning
                             Damage


                           Normal cell


                Structural and/or Biochemical lesion
                                              Fatty change (liver)
              Cloudy swelling (cytoplasmic breakdown)


             Vacuolar degeneration (escape of enzymes)


                      Hydropic degeneration


                           DEAD CELL
                             necrosis
Cytoplasmic changes                            Nuclear changes
SOME CAUSES OF NECROSIS


Severe pathological perturbations (eg ischaemia,
                                     infarcts, atheroma )


Severe environmental trauma (eg injury, toxic insult )

Degradative change
(excessive liquid discharge)




                               eg
Caseating granuloma of TB
CELL DEATH IN
  TUMOURS
NECROSIS
Necrosis in colorectal carcinoma
Why necrosis occurs in malignant tumours
Necrosis near a non-patent blood vessel
         Liver: piecemeal necrosis

Widespread apoptosis with secondary necrosis
PHYSIOLOGICAL DIFFERENCES

                 BETWEEN

  NECROSIS AND APOPTOSIS
(Necrosis is in anoxic areas, apoptosis in oxic zones)
             Plan of the events of apoptosis




(Wyllie A. 1982, in ‘Cell Death in Biology and Pathology’, Bowen and Lockshin)
       APOPTOSIS


 metazoan cell removal kit
kills non-required cells
 removes the evidence – fast

BETTER DEAD THAN WRONG
1.   Apoptotic cell




2.   Apoptotic bodies



3.   Phagocytosis of
     apoptotic bodies


4. Teleolysosome
Apoptosis near a mitotic figure
Apoptosis in
crypts after
treatment with
AraC
Apoptosis in sunburnt skin
Apoptosis in the glomerulus
The annexin-V technique
Accumulation of mutant p53 after UV skin damage
Apoptosis and viral infection
MECHANISMS OF
 APOPTOSIS
Characteristic DNA
laddering in apoptosis

Cleavage is at the sites
between nucleosomes
yielding discrete fragments
of integer multiples.

The number of base pairs
of one nucleosome is in
the order of 200.
Internucleosome
   cleavage
Wyllie (1998).      An endonuclease at last!
Nature 391 20-21
                     Caspase activated DNAase CAD
                                   Apoptotic stimuli

               Caspase activation
                   DEATH DOMAINS (D D)
                     D D


                                    Base
                                    pair
                                 integers
ACRONYMS IN APOPTOSIS
Caspases, particularly 8 & 9
                (nematode ced-3)

Cytochrome c activates Apaf-1

Apaf-1         apoptosis-activating factor
               (nematode ced-4)


Two major Death Inducing Signalling Complexes
                 (DISCs)

1. Apaf-1/procaspase 9/dATP/cytochrome c

2. Fas/FasL/FADD/pro-caspase 8
Death Inducing Signalling Complexes


               DISCs

• Cyt   c + Apaf-1 + procaspase-9 + dATP


• FasL + Fas + FADD + procaspase-8
(activated by cytochrome c)
    Initial observations in C. elegans
Reduction           Cells had




    Horweiz – Nobel prize 2002
Mammalian homologues of
   nematode genes


 ced-9 a gene for life


 23% homology with bcl-2
Interleukin 1b converting enzyme (ICE)
Mammalian homologues have been searched for from gene
                       sequence libraries
(Fas)
             The general diagram of Fas ligation
             and the cascade




Caspase activated DNAase
and its inhibitor
ICE-like proteases later unified by the name ‘caspases’
Mechanism of induction of apoptosis in
cytotoxic T cell killing via granzyme B
             and caspases
(activated by cytochrome c)
COFFEE TIME!
CASPASES
           CASPASES

  The caspases make up a family of cytoplasmic
  lytic enzymes, stimulated by and active in the
  process of apoptosis.

  They are the effector molecules of the
  morphological manifestation of apoptosis




(formerly known as ICE-like proteases etc)
CASPASE TARGETS (death substrates)


       DNA repair proteins

       Structural proteins

      Oncoproteins

      ICAD
Renaming of the family of
  cysteine proteases


All known caspases possess
an active-site cysteine and
cleave substrates at Asp-Xxx
bonds – after the aspartic
acid.
           The caspase cascade
     Inactive
PD

     D      D
                                      Death Substrates
         Active

                PD

                     D   D



                             PD

                                  D   D
    Activation of apoptosis in mammals
    {Li et al (1991) Cell 91 479-489}

            Apaf-2                                          ATP
         Cytochrome c
                                       ced-4
                                                     WD40 REPEATS


         Bcl-2
              D

                                               D     Activated caspase-9
Apaf-3 = procaspase-9

                 procaspase-3           p20    p12
                 activated caspase-3
THE bcl-2 FAMILY
   THE Bcl-2 PROTEIN FAMILY


Some members PROMOTE apoptosis
Bax, Bad, Bid, Bik, Hrk, Egl-1, Bcl-x small,
Bak

Other members are ANTI-APOPTOTIC
Bcl-2, Bcl-x large
(C. elegans equivalent = ced-9)
    Cyclin B- cdk1


                              Cyclin D-cdk4/6

                              Cyclin E cdk2
Cyclin A-cdk1 is a
ubiquitous inhibitor          Cyclin A-cdk2
of the cell cycle.

It is encoded by the
Gene Cip1

                               p53 is negatively
                              regulated by Mdm2




   ASPECTS OF p53 CELL CYCLE CONTROL
                   globular




                                    pore




The Bax dimer is pro-apoptotic; the pore allows exit of cytochrome c
                        to initiate apoptosis
WHICH MOLECULES FORM CHANNELS in vivo?


• Bax

• Bcl-2/Bclx-L may prevent transition of Bax from
  globular to pore-forming state

• The BH3 branch (Bik, Bad, Hrk) don’t form pores

• BH3 proteins are inhibitors of survival proteins
The BH4 domain is requisite for
    anti-apoptotic activity
Growth factor initiation of Bad and Bcl-2
              interactions
Growth factor initiation
of Bad and Bcl-2
interactions
Apoptosome

Pro-caspase-3
Apaf-1
Bcl-2

(cytochrome c would activate Apaf-1
 to cause apoptosis.
 Bcl-2 activation would prevent
 apoptosis)
                    CARD = caspase recruitment domain




                             apoptosis proceeds




Bcl-x large is anti-apoptotic
       Fas(CD95)


       and
Fas ligand (FasL)
Fas/FasL
Fas is a cell surface receptor. When bound
by Fas-ligand, there is trimerisation that
initiates the downstream events of
apoptosis
Fas/FasL
Various normal tissues express functional
Fas.

FasL expression by carcinoma cells
induces apoptosis in normal cells proximal
to the site. This might facilitate metastasis
Plan of Fas ligation, trimerisation
 and activation of apoptosis
The general diagram of Fas ligation
and the cascade
Fas and Fas ligand activation of apoptosis
are of major importance in both malignant
diseases and in non-malignant diseases.

Fas and FasL expression in cells of the
immune system has widespread implications
(SLE for example has defective Fas)

				
DOCUMENT INFO