Difference Between Apoptosis and Senescence

Main Difference – Apoptosis vs Senescence

Apoptosis and senescence are two types of developmental programs of cells to die. Apoptosis is a pre-defined and tightly regulated process. Senescence is responsible for the cell’s aging. Apoptosis is involved in the cell death in order to balance the cell number in the organism. Pathological stimuli may also cause apoptosis-like infections. Senescence is caused by damages in the intercellular structures as well as the cell’s aging programs. During senescence, the cell loses its power of proliferation and growth. The main difference between apoptosis and senescence is that apoptosis is a programmed cell death whereas senescence is the deterioration with age.

This article looks at, 

1. What is Apoptosis
       – Definition, Characteristics, Process
2. What is Senescence
       – Definition, Characteristics, Process
3. What is the difference between Apoptosis and Senescence

What is Apoptosis

Apoptosis is a pre-planned cell death (PCD), which is a regular and controlled mechanism where the cell actively is involved in its own death. Hence, apoptosis is also called the cellular suicide. Apoptosis is considered as a part of cellular multiplication and turnover, maintaining the balance of the number of cells in the body. Thus, each cell in the body of a multicellular organism consists of a pre-defined lifespan. As an example, the lifespan of red blood cells in the human body is 120 days.

During apoptosis, condensation of chromatin is considered as a hallmark. The cell shrinks and becomes fragmented during apoptosis. The integrity of the plasma membrane is kept as it is by forming apoptotic bodies, surrounding the cellular contents by the plasma membrane. Thus, cellular contents are not released into the extracellular milieu in order to generate an inflammatory response. Induced apoptosis by scFv 4D5-dibarnase for 72 h is shown in figure 1. Apoptosis is described by membrane blebbing after the induction.

Figure 1: Induced Apoptosis

What is Senescence

Senescence is the deterioration with age. Due to senescence, the cell ages. Aging is the time-related deterioration of cell’s physiological functions, required for survival and fertility. During senescence, actively proliferating cells are arrested at G1 phase of the cell cycle due to a variety of stress. But, these cells maintain their functions as it is other than proliferation. Genes in the genome are involved in the regulation of senescence, determining the lifespan of a cell. Usually, the lifespan of a human is 121 years. But, it can be changed due to the alteration of genes and diet. In angiosperms, flowering and senescence are two closely related processes. Fruit ripening is an example of senescence. Aging is caused by oxidative damage, genetic instability like DNA damage, mitochondrial genome damage, telomere shortening and genetic aging programs. Ginkgo aging is shown in figure 2.

Figure 2: Ginkgo Aging

Difference Between Apoptosis and Senescence

Definition

Apoptosis: Apoptosis is the programmed cell death.

Senescence: Senescence is the deterioration with age.

Role

Apoptosis: Apoptosis helps to balance the cell number within the organism.

Senescence: Due to the senescence, the cell ages.

Significance

Apoptosis: Chromosome condensation is the hallmark of apoptosis.

Senescence: The irreversible arrest of cell proliferation is the hallmark of senescence. 

Caused by

Apoptosis: Apoptosis is caused by both physiological and pathological stimuli.

Senescence: Senescence is caused by oxidative damage, genetic instability like DNA damage, mitochondrial genome damage, telomere shortening and genetic aging programs.

Regulation

Apoptosis: Apoptosis is regulated by an intracellular proteolytic cascade.

Senescence: Senescence is regulated by the genes involved in the cell’s aging.

Conclusion

Both apoptosis and senescence are involved in the cell death in multicellular organisms. Apoptosis is a pre-defined cell death, which can be induced by physiological stimuli. Apoptosis can be induced by pathological reasons like infections as well. It is a tightly regulated process by enzymes like caspase. Senescence is the deterioration of cells due to functioning. It can be caused by damage to the intercellular structures as well as the genes,  involved in the regulation of aging. The main difference between apoptosis and senescence is the causes involved in the processes.

 Reference:
1. Alberts, Bruce. “Programmed Cell Death (Apoptosis).” Molecular Biology of the Cell. 4th edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 02 Apr. 2017.
2. Gilbert, Scott F. “Aging: The Biology of Senescence.” Developmental Biology. 6th edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 02 Apr. 2017.

Image Courtesy:
1. “Apoptosis induced by scFV 4D5-dibarnase” By Edelweiss E, Balandin TG, Ivanova JL, Lutsenko GV, Leonova OG, Popenko VI, Sapozhnikov AM, Deyev SM – Modified from Edelweiss E, Balandin TG et al Barnase as a New Therapeutic Agent Triggering Apoptosis in Human Cancer Cells PLoS One. 2008 Jun 18;3(6):e2434. (CC BY 2.5) via Commons Wikimedia
2. “Ginkgo senescence” By Bernskbarn – Own work (CC BY-SA 4.0) via Commons Wikimedia