Programmed cell death Programmed cell death (PCD) is cell death mediated by an intracellular program. PCD is carried out in a regulated
process, which usually confers advantage during an organism's
life-cycle. For example, the differentiation of fingers and toes in a developing human embryo occurs because cells between the fingers
apoptose; the result is that the digits separate. PCD serves fundamental functions during both plant and
metazoa (multicellular animals) tissue development.
Apoptosis Apoptosis is the processor of programmed cell death (PCD) that may occur in
multicellular organisms. Certain key proteins primarily employed in the
repair of DNA damage can also induce apoptosis when
DNA damage exceeds the cell’s repair capability. These dual role proteins protect against proliferation of unstable damaged cells that might lead to cancer.
Autophagy Autophagy is
cytoplasmic, characterized by the formation of large
vacuoles that eat away
organelles in a specific sequence prior to the destruction of the
nucleus.
Macroautophagy, often referred to as
autophagy, is a
catabolic process that results in the
autophagosomic-
lysosomal degradation of bulk
cytoplasmic contents, abnormal protein aggregates, and excess or damaged
organelles. Autophagy is generally activated by conditions of
nutrient deprivation but has also been associated with
physiological as well as
pathological processes such as development, differentiation,
neurodegenerative diseases,
stress,
infection and
cancer.
Other variations of PCD Other pathways of programmed cell death have been discovered. Called "non-apoptotic programmed cell-death" (or "
caspase-independent programmed cell-death"), these alternative routes to death are as efficient as apoptosis and can function as either backup mechanisms or the main type of PCD. Some such forms of programmed cell death are
anoikis, almost identical to apoptosis except in its induction;
cornification, a form of cell death exclusive to the eyes;
excitotoxicity;
ferroptosis, an iron-dependent form of cell death and
Wallerian degeneration. Plant cells undergo particular processes of PCD similar to autophagic cell death. However, some common features of PCD are highly conserved in both plants and metazoa.
Activation-induced cell death (AICD) is a programmed cell death caused by the interaction of
Fas receptor (Fas, CD95)and Fas ligand (FasL, CD95 ligand). It occurs as a result of repeated stimulation of specific
T-cell receptors (TCR) and it helps to maintain the
peripheral immune tolerance. Therefore, an alteration of the process may lead to
autoimmune diseases.
Mitotic catastrophe is an oncosuppressive mechanism that can lead to cell death that is due to premature or inappropriate entry of cells into mitosis. It is the most common mode of cell death in cancer cells exposed to
ionizing radiation and many other anti-cancer treatments.
Immunogenic cell death or immunogenic
apoptosis is a form of cell death caused by some cytostatic agents such as
anthracyclines, oxaliplatin and bortezomib, or
radiotherapy and
photodynamic therapy (PDT).
Pyroptosis is a highly inflammatory form of programmed cell death that occurs most frequently upon infection with intracellular pathogens and is likely to form part of the antimicrobial response in myeloid cells.
PANoptosis is an innate immune, lytic cell death pathway initiated by innate immune sensors and driven by caspases and
RIP kinases through PANoptosome complexes. To date, several PANoptosome complexes have been characterized, including
ZBP1-,
AIM2-,
RIPK1-,
NLRC5-/NLRP12-, and NLRP3-PANoptosomes. PANoptosis is critical in innate immune responses for host defense, but it has also been implicated in inflammation and pathology in inflammatory diseases, infections, and cancers.
Phagoptosis is cell death resulting from a live cell being phagocytosed (i.e. eaten) by another cell (usually a phagocyte), resulting in death and digestion of the engulfed cell. Phagoptosis can occur to cells that are pathogenic, cancerous, aged, damaged or excess to requirements.
Necrotic cell death Necrosis is cell death where a cell has been badly damaged through external forces such as trauma or infection and occurs in several different forms. It is the sum of what happens to cells after their deaths. In necrosis, a cell undergoes swelling, followed by uncontrolled rupture of the cell membrane with cell contents being expelled. These cell contents often then go on to cause inflammation in nearby cells. A form of programmed necrosis, called
necroptosis, has been recognized as an alternative form of programmed cell death. It is hypothesized that necroptosis can serve as a cell-death backup to apoptosis when the apoptosis signaling is blocked by endogenous or exogenous factors such as viruses or mutations. Necroptotic pathways are associated with death receptors such as the tumor necrosis factor receptor 1.
Identification of cell death was previously classified based on morphology, but in recent years switched to molecular and genetic conditions. == See also ==