Cell death Flashcards
How were the different types of cell death FIRST classified?
By morphological traits
Why does classification of different types of cell death require more than just studying the morphological traits?
Apparently similar cell death morphocytes often actually share a LOT of functional, biochemical and immunological heterogeneity AND the presence of specific morphological features is not enough to establish a causal link between a given process and cellular demise
What are the advantages of using biochemical methods for assessing cell death over morphological techniques?
Quantitative - therefore less prone to misinterpretation
What is a drawback of using biochemical rather than morphological methods for assessing cell death?
1) cell death pathway that is often associated with a certain biochemical pathway may occur in the absence of that pathway 2) a cell death-associated pathway may develop at a sub-lethal/transient level, which does not lead to cell death
According to morphological appearance, what are the four classes of cell death?
Apoptosis Necrosis Autophagy Mitosis-associated (Mitotic catastrophe?)
According to which cellular features may cell death be classified?
1) morphological appearance 2) enzymological criteria 3) functional aspects 4) immunological characteristics
When is a cell ‘dead’?
Dying cells are engaged in a process that is reversible until a first irreversible phase (or ‘point of no return’) is passed
What are the different functional aspects dying cells may be classified by?
1) Programmed/accidental 2) Physiological/pathological
Why is ‘caspase activation’ not considered a ‘point of no return’ in cell death?
Because caspases can be activated in non-lethal pathways
What are the different ‘enzymological criteria’ cell death may be classified by?
With/without the involvement of nucleases such as caspases, calpains, cathepsins, transglutaminases
Why can ‘loss of mitochondrial transmembrane potential’ not be used as a marker of cell death?
Because the mitochondrial transmembrane potential can be dissipated by protonophores without progression to immediate cell death
Give three molecular/morphological features by which dead cells can be defined
1) Loss of plasma membrane integrity 2) Cell fragmentation 3) Engulfment by adjacent cells
What is meant by ‘loss of plasma membrane integrity’?
The plasma membrane has broken down, resulting in the loss of the dead cell’s identity
How can ‘loss of plasma membrane integrity’ be detected?
Immunofluorescence (IF) microscopy and/or fluorescence-activated cell sorter (FACS) to assess the exclusion of vital dyes, in vitro (e.g. TRYPAN BLUE)
What does ‘cell fragmentation’ involve?
The cell (including its nucleus) has undergone complete fragmentation into discrete bodies (usually referred to as apoptotic bodies)
How can ‘cell fragmentation’ be detected?
Immunofluorescence (IF) microscopy Fluorescence-activated cell sorter (FACS) quantification of hypodiploid events (sub-G1 peak)
What does ‘engulfment by adjacent cells’ involve in cell death?
The corpse or its fragments have been phagocytosed by neighbouring cells
How can ‘engulfment by adjacent cells’ be detected?
Immunofluorescence (IF) microscopy Fluorescence-activated cell sorter (FACS) co-localisation studies
List 4 ‘proposed points of no return’ to define dying cells NB. some of these may not actually lead to immediate cell death
1) massive activation of caspases 2) mitochondrial transmembrane potential (Dcm) dissipation 3) mitochondrial outer membrane permeabilisation (MMP) 4) phosphatidylserine (PS) exposure
In the absence of a clearly defined biochemical event that can be considered as the point-of-no-return, what criteria does the NCDD propose a cell should meet in order to be defined as ‘dead’?
At least one of the following molecular/morphological criteria: (1) the cell has lost the integrity of its plasma membrane, as defined by the incorporation of vital dyes (e.g., PI) in vitro; (2) the cell, including its nucleus, has undergone complete fragmentation into discrete bodies (which are frequently referred to as ‘apoptotic bodies’); (3) its corpse (or its fragments) has been engulfed by an adjacent cell in vivo.
In ‘ACTIVE’ cell death, what do: a) programmed, and b) regulated cell death involve?
a) programmed: refers to physiological instances of cell death that occur during development or tissue homeostasis b) regulated: engages a dedicated cellular signalling pathway
Using the morphological criteria for distinguishing different types of cell death, give three types of cell death that are considered ‘ACTIVE’ (i.e. the cell has committed suicide in a regulated and/or programmed way)
1) apoptosis 2) autophagy 3) cornification
Give 7 features of apoptotic cell death
1) rounding-up of the cell 2) retraction of pseudopodes 3) reduction of cellular and nuclear volume (pyknosis) 4) nuclear fragmentation (karyorrhexis) 5) minor modification of cytoplasmic organelles 6) plasma membrane blebbing 7) engulfment by resident phagocytes, in vivo
Give 4 features of autophagy
1) Lack of chromatin condensation 2) Massive vacuolisation of the cytoplasm 3) Accumulation of (double-membraned) autophagic vacuoles 4) Little/no uptake by phagocytic cells, in vivo
Give 5 features of cornification
1) Elimination of cytosolic organelles 2) Modifications of plasma membrane 3) Accumulation of lipids in F and L granules 4) Extrusion of lipids in the extracellular space 5) Desquamation (loss of comeocytes) by protease activation
Whilst apoptosis, autophagy and cornification are considered ‘ACTIVE’ cell death, what is a form of ‘PASSIVE/ACCIDENTAL’ cell death?
Necrosis
Give 4 features of necrosis
1) Cytoplasmic swelling (oncosis) 2) Rupture of plasma membrane 3) Swelling of cytoplasmic organelles 4) Moderate chromatin condensation
Of 1090 initial somatic cells, how many are eliminated by apoptosis?
131
In C.Elegans, what is the homolog for caspase?
CED-3
In C.Elegans, what binds to and activated the caspase homolog, CED-3?
CED-4 (Apaf-1 homolog)
What enzyme is the C.Elegans ‘CED-4’ a homolog for?
Apaf-1
What is the homolog for BCL-2 in C.Elegans?
CED-9
