Apoptosis

Cell apoptosis, sometimes called programmed cell death, is a cellular self-destruction method to remove old and damaged cells during development and aging to protect cells from external disturbances and maintain homeostasis. Apoptosis also occurs as a defense mechanism such as in immune reactions or when cells are damaged by disease or noxious agents.

Apoptosis is controlled by many genes and involves two fundamental pathways: the extrinsic pathway, which transmits death signals by the death receptor (DR), and the intrinsic or mitochondrial pathway. The extrinsic apoptotic pathway is activated by the binding of the death ligand to DRs, including FasL, TNF-α, and TRAIL, on the plasma membrane. The DR, adaptor protein (FADD), and associated apoptosis signaling molecule (caspase-8) form the death-inducing signaling complex (DISC), thus leading to the activation of the effector caspase cascade (caspase-3, -6, and -7). The mitochondria-mediated intrinsic apoptosis pathway is regulated by Bcl-2 family proteins, including proapoptotic (Bid, Bax, Bak) and antiapoptotic proteins (Bcl-2, Bcl-xL).

Abnormalities in cell apoptosis can be a significant component of diseases such as cancer, autoimmune lymphoproliferative syndrome, AIDS, ischemia, and neurode-generative diseases. These diseases may benefit from artificially inhibiting or activating apoptosis. A short list of potential methods of anti-apoptotic therapy includes stimulation of the IAP (inhibitors of apoptosis proteins) family of proteins, caspase inhibition, PARP (poly [ADP-ribose] polymerase) inhibition, stimulation of the PKB/Akt (protein kinase B) pathway, and inhibition of Bcl-2 proteins.

Ferroptosis and necroptosis are recently recognized forms of regulated cell death that differs considerably from apoptosis. Misregulated ferroptosis or necroptosis have also been implicated in multiple physiological and pathological processes, including cancer cell death, neurotoxicity, neurodegenerative diseases, etc.

References:
[1] Susan Elmore. Toxicol Pathol. 2007; 35(4): 495–516.
[2] Cao L, et al. J Cell Death. 2016 Dec 29;9:19-29.
[3] Dasgupta A, et al. Int J Mol Sci. 2017 Jan; 18(1): 23.
[4] Xie Y, et al. Cell Death Differ. 2016 Mar;23(3):369-79.