Fig. 2

Apoptosis-related pathway. There are two main ways of apoptosis. In the extrinsic pathway, the death receptor binds to its corresponding ligands, including Fas, TNFR1, DR4, and DR5, and the corresponding ligands include FasL, TNF-α, and TNF-associated apoptosis-inducing ligand (TRAIL), which activate caspase 8 and subsequently caspase 3. It leads to apoptosis. In the intrinstic pathway, when DNA is damaged, the pro-apoptotic proteins Bax and Bak are activated, and the anti-apoptotic proteins Bcl-2 and Bcl-xL are inhibited. Subsequently, a series of apoptotic factors are released, including cytochrome c, APAF-1, and procaspase 9, which form a complex called the apoptosome. This complex can activate caspase 9, which in turn activates caspase 3, and ultimately leads to apoptosis