Difference Between Autophagy and Apoptosis

Key Difference – Autophagy vs Apoptosis

Cell death is a natural phenomenon occurring in all living cells. It is a type of defense mechanism and is mediated byimmune responses. Cell death can take place mainly in two different forms: programmed cell death or cell death resulting from harmful components such asradiation, infectious agents or different chemicals. Programmed cell death is a resultant injury of cellular components like cellular organelles, cellular proteins, and other cellular biomolecules. This is an irreversible process. The cells lose its structural and functional properties upon programmed cell death and cannot be retrieved. Autophagy and Apoptosis are two methods of programmed cell death. Both processes are important in development and normal physiology.Autophagy is the cell death process mediated bylysosomes, which termed as lysosomal degradation. Apoptosis is the programmed cell death that takes place when the cells commit suicide by activating an intracellular death program.This is the key difference between autophagy and apoptosis.

CONTENTS

1.Overview and Key Difference
2.What is Autophagy
3.What is Apoptosis
4.Similarities Between Autophagy and Apoptosis
5.Side by Side Comparison – Autophagy vs Apoptosis in Tabular Form
6.Summary

What is Autophagy?

Autophagy is acatabolicmechanism during which cells degrade the dysfunctional and unnecessary cellular components by a lysosome-mediated action. During autophagy, the organelles to be degraded are surrounded by a double membrane, forming a structure called the autophagosome. The autophagosome then fuses with the lysosomes in thecytoplasmand form the autolysosome. Then the degraded organelles trapped inside the autolysosome are degraded by the activity of lysosomal hydrolases. This type of autophagy is known as macrophagy.

There are two other types of autophagy: micro-autophagy, and chaperone-mediated autophagy. In micro-autophagy, an autophagosome is not formed. Instead, the autolysosome is directly formed. In chaperone-mediated autophagy, targeted proteins are subjected to degradation via chaperone proteins. This is a specific type of autophagy.

Autophagy is regulated by a signaling pathway mediated bytyrosine激酶,is largely driven by nutrient-deprived conditions andhypoxia.

Autophagy is much studied at present due to its role in health and physiology of cancer, heart diseases, andautoimmune diseases.

What is Apoptosis?

Apoptosis is programmed cell death. A cell undergoes apoptosis without causing any damage to other cells or other cellular components. During apoptosis, the cell begins to shrink and condense which is followed by the degeneration of the cytoskeleton. This results in the disassembly of the nucleus andnuclear DNAis degraded upon exposure. In most apoptotic pathways, the cell membrane is destroyed and the cell become fragmented. Thenphagocytic cellssuch asmacrophagesidentify fragmented cell parts and remove them from the tissues.

The apoptotic intracellular machinery is mediated by a cascade of protein-mediated reactions. This apoptotic mechanism is dependent on a special family of proteases,enzymesthat degrade proteins. These proteins are termed as Caspases. Caspases have a characteristiccysteineamino acid at their active site. Caspases also have a characteristic cleavage site which consists of theamino acid, aspartate. Procaspases are the precursors of caspases, and the procaspases are activated by the cleavage at aspartate sites. Activated caspases can then cleave and degrade other proteins in the cytoplasm as well as in the nucleus, resulting in cellular apoptosis. There are two main types of apoptotic Caspases: initiator caspases and effector caspases. Initiator caspases are involved in commencing the cascade of reactions. Effector Caspases are involved in the disassembly of the cell and completion of the apoptotic pathway.

What are the Similarities Between Autophagy and Apoptosis?

• Both result in programmed cell death.
• Both are natural phenomena.
• Both processes do not cause damage to other cells or cellular components.
• Both are important in development and normal physiology.
• Both are important in understanding the cellular basis of different pathological conditions including cancer and immune system related disorders.

What is the Difference Between Autophagy and Apoptosis?

Autophagy vs Apoptosis
Autophagy is the cell death process mediated by lysosomes.	Apoptosis is programmed cell death mediated by proteases known as Caspases.
Subtypes
Macrophagy, Microphagy, and Chaperon mediated autophagy are types of autophagy.	Apoptosis does not have subtypes.
Action
Autophagy occurs via lysosome degradation by lysosomal hydrolases.	Apoptosis occurs through proteases known as Caspases which include the initiator Caspases, and effector Caspases degrade the proteins.
Special Features
Autophagy process forms autophagosome, autolysome or chaperone bound complexes during the process.	The cells begin to condense and shrink followed by destruction which is catalyzed by Caspases in apoptosis.
Regulation
Regulation of autophagy occurs by a signaling pathway mediated by tyrosine kinase.	Many different proteins are involved in the regulation of apoptosis.

Summary – Autophagy vs Apoptosis

There are many challenges in understanding the underlined mechanisms of both autophagy and apoptosis, especially the regulatory mechanisms. Autophagy involved in lysosomal degradation, whereas apoptosis is programmed cell death mediated by proteases. This is the difference between autophagy and apoptosis. Both participate in cell death and protect other cells and organs from oxidative stress caused by damaged cells.

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References:

1. Alberts, Bruce. “Programmed Cell Death (Apoptosis).” Molecular Biology of the Cell. 4th edition., U.S. National Library of Medicine, 1 Jan. 1970,Available here. Accessed 13 Sept. 2017.
2. Glick, Danielle, et al. “Autophagy: cellular and molecular mechanisms.” The Journal of pathology, U.S. National Library of Medicine, May 2010,Available here. Accessed 13 Sept. 2017.
3.Rhorburn,安德鲁。“细胞凋亡和自噬:注册ulatory connections between two supposedly different processes.” Apoptosis: an international journal on programmed cell death, U.S. National Library of Medicine, Jan. 2008,Available here. Accessed 13 Sept. 2017.

Image Courtesy:

1. “Autophagy” By Cheung and Ip – Molecular Brain, Biomed Central (CC BY 3.0) viaCommons Wikimedia
2. “Structural changes of cells undergoing necrosis or apoptosis” By National institute on alcohol abuse and alcoholism (NIAAA) – File:Structural changes of cells undergoing necrosis or apoptosis.gif; (pubs.niaaa.nih.gov), (Public Domain) viaCommons Wikimedia