Apoptosis, or programmed cell death, occurs through three primary pathways. These methods ensure that cells die in a controlled manner, playing a crucial role in development and maintaining tissue health.
Apoptosis Pathways
Here are the three main methods through which apoptosis is induced, according to the provided reference [2-3]:
-
Mitochondrial (Intrinsic) Pathway:
- This pathway is also known as the cellular or apoptosis intrinsic pathway.
- It involves triggering apoptosis by affecting the functionality of mitochondria.
- Various cellular stresses, such as DNA damage, can initiate this pathway.
- Example: If the cell’s DNA is severely damaged, the mitochondria releases molecules like cytochrome c which activates a cascade of proteins that results in cell death.
-
Death Receptor (Extrinsic) Pathway:
- This pathway, also known as the apoptosis extrinsic pathway, begins with direct signal transduction.
- Adaptor proteins transmit the apoptotic signal.
- This involves cell surface death receptors that bind to specific ligands to initiate apoptosis.
- Example: Death receptors, such as Fas, bind to Fas ligands, resulting in the activation of caspases that induce cell death.
-
Perforin/Granzyme Pathway:
- This method uses perforin and granzymes.
- Cytotoxic immune cells, such as natural killer (NK) cells and cytotoxic T lymphocytes (CTLs), use this pathway.
- Perforin creates pores in the target cell's membrane, allowing granzymes to enter and induce apoptosis.
- Example: During an immune response to a virus, CTLs use this pathway to eliminate virus-infected cells by using perforin to open a passage in the cells and granzyme to trigger cell death.
Table Summary
| Pathway | Initiating Factor | Mechanism | Primary Players |
|---|---|---|---|
| Mitochondrial (Intrinsic) | Cellular Stress (DNA damage, etc.) | Affects mitochondria functionality causing the release of molecules | Mitochondria, cytochrome c, caspases |
| Death Receptor (Extrinsic) | Ligand binding to death receptors | Direct signal transduction via adaptor proteins to activate caspases | Death receptors (e.g., Fas), adaptor proteins, caspases |
| Perforin/Granzyme | Cytotoxic immune cell targeting | Perforin creates pores; granzymes enter and induce apoptosis | Perforin, granzymes, cytotoxic immune cells (NK cells, CTLs) |
Understanding these different pathways is crucial for studying cell biology and developing therapeutic strategies. The careful orchestration of these methods is important for maintaining balance within the body.
