Table 1.

The general features of chondrocyte death in osteoarthritis.

Type of death Morphological features	Apoptosis	Chondroptosis	Necrosis	Nercoptosis	Autophagic death	Pyroptosis	Ferroptosis
Cell morphology	Shrinkage	Shrinkage	Swelling (oncosis)	Shrinkage	Shrinkage	Swelling	Shrinkage
Cytoplasmic membrane	Blebbing but intact	Vesicle blebs	Disrupted	Disrupted	Participate to autophagosome formation	Disrupted	Disrupted
Cytoplasm	Densed	Densed	Granulation	Decomposition	Decomposition	Decomposition	Decomposition
Increase of organelles	No	prominent expansion of the rough endoplasmic reticulum (RER) and the Golgi apparatus	No	No	No	No	No
Nucleus	Fragmentation into apoptotic bodies	Convoluted nucleus Nuclear condensation	Nuclear condensation (pyknosis)	Decomposition	Intact until late stages	Nuclear condensation (pyknosis)	Intact until late stages
Chromatin	Marginal condensation at the nucleus membrane and aggregate in larger masses	Patchy condensation throughout the nucleus	Fragmented	Fragmented	Absence of condensation	Fragmented	Fragmented
DNA	Intranucleosomal cleavage-DNA laddering	Cleaved	Random cleavage DNA Smear	Random cleavage DNA Smear	DNA fragmentation occurs very late	Random cleavage DNA Smear	Random cleavage DNA Smear
Apoptotic bodies	Yes	Cellular remnants and vesicules	Cell explosion	Cell explosion	No	No	No
Autophagic vacuoles	No	Frequent	No	No	Abundant	No	No
Rough endoplasmic reticulum		Prominent expansion	Swelling	Swelling	Protuding、engulfing	Swelling	Swelling
Golgi apparatus	No increase	Increase in early stages	No increase	No increase	Enlargement	No increase	Enlargement
Behavioral characteristics
Inflammation	No	Not precised	Yes	Yes	No	Yes	Yes
ER	No enlargement	Increase in amount and expansion of lumen	No enlargement	No enlargement	Enlargement	No enlargement	Enlargement
Release of cellular contents into intracellular space	No	No	Yes	Yes	No	Yes	Yes
Elimination	Phagocytosis of apoptotic bodies	Phagocytosis-independent self destruction	General lysis	General lysis	Auto-elimination	General lysis	General lysis
Occurs in physiological situations	Yes	Yes	Yes	Yes	Yes	No	Yes
Mechanistic features
Lysosomal enzyme	Inside apoptotic bodies	Inside cytoplasmic ‘islands’ or autophagic vacuoles	Leakage	Leakage	Inside autophagic vacuoles	Leakage	Leakage
Caspase-dependent	Yes	Yes	No	No	No	No	No
Energy-dependent	Yes	Not precised	No	No	Yes	No	No