Difference Between Apoptosis and Pyroptosis

Key Difference – Apoptosis vs Pyroptosis
 

Apoptosis and pyroptosis are cell death mechanisms found in eukaryotic organisms. Apoptosis is a common, genetically conserved suicide mechanism employed by multicellular organisms, which is highly regulated and not harmful since it does not involve rapid cell lysis. Pyroptosis is a proinflammatory programmed cell death by cell lysis followed by an aggressive activation of inflammatory caspase 1. This is the key difference between apoptosis and pyroptosis.

CONTENTS
1. Overview and Key Difference
2. What is Apoptosis
3. What is Pyroptosis
4. Side by Side Comparison – Apoptosis vs Pyroptosis
5. Summary

What is Apoptosis?

Cell division and cell death are highly regulated in multicellular organisms. Apoptosis is a process where unwanted cells are subjected to programmed cell death. It is a genetically conserved cell suicide mechanism executed by the cell itself (intracellular). This process is very crucial for normal development, maintenance of the tissue homeostasis and function in multicellular organisms. Tissues will refresh with new cells once they eliminate unwanted, damaged and harmful cells by apoptosis. Apoptosis does not harm neighboring tissues or cells like necrosis. In a developing or an adult human, a remarkable number of cells die per hour by apoptosis. For example, billions of cells in the intestine and bone marrow of a healthy person die within an hour. It is said that for an average adult, 50 to 70 billion cells die a day.

Apoptosis is characterized by different biochemical events, leading to cell morphology changes and cell death. The ultimate cell death will follow a series of events including cell shrinkage, cell fragmentation, nuclear envelope disassembly, cytoskeleton collapse, apoptotic body release and engulfment of apoptotic bodies, etc. All these events will be governed by the proteolytic enzymes called caspases. These enzymes can be divided into three major groups: killer proteins, destruction proteins, and engulfment proteins.

Multicellular organisms have two distinct apoptosis pathways; intrinsic (mitochondrial pathway) and extrinsic (death receptor pathway) as shown in figure 01. The intrinsic pathway is initiated within the cell by mitochondrial events that lead to diverse non-receptor mediated stimuli to cause cell death. Extrinsic pathway occurs when the extracellular death ligands bind with death receptors and induce the caspase activity to cause cell death. Both pathways ultimately lead the irreversible cell death.

Apoptosis is very important in destroying oncogenic cells to prevent cancer development.

What is Pyroptosis?

Pyroptosis refers to a proinflammatory programmed cell death also known as caspase 1 – dependent cell death. This is kind of a sudden programmed cell death, driven by pathological stimuli such as microbial infections, cancers, strokes and heart attacks. It has been identified recently and is distinguished from apoptosis due to its differences in mechanism, characteristics, and outcome. Caspase 1 is the main enzyme that recognizes the death factor and activates the inflammatory cytokines causing the plasma membrane to rupture suddenly and release proinflammatory contents leading to rapid cell death as shown in figure 02.

What is the difference between Apoptosis and Pyroptosis?

Apoptosis vs  Pyroptosis
Apoptosis is a common, genetically conserved suicide mechanism employed by multicellular organisms, which is highly regulated.	Pyroptosis is a proinflammatory programmed cell death by cell lysis followed by an aggressive activation of inflammatory caspase 1.
Cell Architecture
This causes a series of morphological and biochemical events leading to the alteration of cell architecture.	Cell architecture is not altered. This process involves the production of inflammatory contents, rupture of plasma membrane and cell lysis.
Authority
Apoptosis is a highly programmed, non-inflammatory process and happens in orderly fashion.	Pyroptosis is a highly inflammatory form of programmed cell death.
Neighboring Cells
This process is not harmful to the neighboring cells.	Neighboring cells are disturbed by the pyroptosis.
Cell Lysis
Cells are not lysed.	Cells are lysed.
Apoptotic bodies vs Inflammatory Content
Apoptotic bodies are formed and removed by phagocytosis.	Inflammatory contents are released to the surrounding.
Involvement of the Enzyme Caspase 1
This process is not involved caspase 1.	Main enzyme is caspase 1.
Enzymes involved in the process
This involves caspase 3, caspase 6, caspase 7 and caspase 8	This involve caspase 1, caspase 4 and caspase 5.

Summary – Apoptosis vs  Pyroptosis

There are different cell death processes found in multicellular organisms such as apoptosis, necrosis, and pyroptosis. Apoptosis is a genetically conserved, non-inflammatory, highly programmed cell suicide mechanism catalyzed by proteolytic enzymes, leading to neat cell death followed by changes in the cell architecture. Pyroptosis is another programmed cell suicide mechanism which is proinflammatory and causes the sudden rupture of the plasma membrane and cell lysis followed by activation of inflammasomes through microbial infections.

Reference:
1.Elmore, Susan. “Apoptosis: A Review of Programmed Cell Death.” Toxicologic pathology. U.S. National Library of Medicine, 2007. Web. 08 Feb. 2017
2.Alberts, Bruce. “Programmed Cell Death (Apoptosis).” Molecular Biology of the Cell. 4th edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 08 Feb. 2017.
3.”Apoptosis in cancer: from pathogenesis to treatment.” Journal of Experimental & Clinical Cancer Research. N.p., n.d. Web. 09 Feb. 2017
4.Nature.com. Macmillan Publishers, n.d. Web. 09 Feb. 2017.
5.Miao, Edward A., Jayant V. Rajan, and Alan Aderem. “Caspase-1 induced pyroptotic cell death.” Immunological reviews. U.S. National Library of Medicine, Sept. 2011. Web. 09 Feb. 2017.

Image Courtesy:
1. “Apop1” By Tsgupta – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Pyroptosis mechanism” By User:Aiyaya (CC BY-SA 3.0) via Commons Wikimedia