What is the Difference Between Aging and Senescence

The main difference between aging and senescence is that aging is an intrinsic feature of living beings as a result of time, environmental factors and genetics, which lead to the progressive loss of physiological integrity, leading to the vulnerability of death whereas senescence is an irreversible form of long-term cell-cycle arrest, caused by excessive intracellular or extracellular stress or damage. Furthermore, 9-10 tentative hallmarks serve as denominators of aging, while senescence or cellular aging is an important denominator of aging.  

Aging and senescence are two biological processes that are intrinsic. They lead to the deterioration of the physiological functions necessary for the survival of an organism and eventually to cell death. 

Key Areas Covered 

1. What is Aging
     – Definition, Features, Importance
2. What is Senescence
     – Definition, Features, Importance
3. What are the Similarities Between Aging and Senescence
     – Outline of Common Features
4. What is the Difference Between Aging and Senescence
     – Comparison of Key Differences

Key Terms 

Aging, Cellular Stress, Cell Cycle Arrest, Senescence

What is Aging 

Aging the gradual deterioration of physiological functions necessary for the survival of an organism. Generally, environmental factors and time are the major factors that result in aging. However, genetic factors also have a role in aging. Ultimately, aging leads to cell death. It also serves as the primary risk factor for major pathologies, including cancer, diabetes, cardiovascular disorders, and neurodegenerative diseases. Therefore, research studies focus on controlling the rate of aging to some extent by altering genetic pathways as well as biochemical processes. 

Figure 1: Aging of the Brain Causes Alzheimer’s Disease

Furthermore, scientists have found nine hallmarks, including genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient-sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. Aging mainly refers to the process of becoming older of humans, animals, and fungi. However, in plants, plant senescence refers to the process of both stress-induced and age-related developmental aging. Moreover, it is also important to note that some simple animals, perennial plants, and bacteria are biologically immortal.  

What is Senescence 

Senescence is the irreversible form of long-term cell cycle arrest. Generally, excessive intracellular or extracellular cell stress or damage result in senescence. It is one of the three responses of the body with a protective role in response to cellular stresses. Therefore, senescence limits the proliferation of damaged cells by arresting the cell cycle. Moreover, the factors affecting senescence include oxidative stress, telomere damage/shortening, DNA damage, mitochondrial dysfunction, chromatin disruption, inflammation, epigenetic dysregulation, and oncogene activation. Apoptosis and autophagy are the other two such cellular responses upon stress.

Figure 2: Plant Senescence

Moreover, in senescence, cells are arrested in the G1 phase of the cell cycle to avoid malignant transformation after undergoing stressful conditions. Although their cell cycle has been arrested, senescent cells are both metabolically and functionally active. On the other hand, there are two types of senescent processes that can occur in the cell – acute and chronic senescence. Generally, acute senescence occurs as a result of a biological process that occurs either during embryonic development, wound healing, or tissue repair. In contrast, chronic senescence occurs as a result of prolonged cellular stress or slowly-occurring macromolecular damage. 

Similarities Between Aging and Senescence 

• In brief, aging and senescence are two biological processes responsible for the deterioration of the physiological functions required for the survival of an organism. 
• Therefore, they are intrinsic processes, which ultimately cause cell death. 
• Moreover, both are irreversible. 

Difference Between Aging and Senescence 

Definition 

Aging refers to the complex biological process which results in cell death as a result of time, environmental factors, and genetics, while senescence refers to the irreversible form of long-term cell-cycle arrest, caused by excessive intracellular or extracellular stress or damage.  

Significance 

Aging leads to the loss of progressive loss of physiological integrity, while senescence leads to the irreversible, long-term cell cycle arrest. 

Correspondence 

There are 9-10 tentative hallmarks serving as denominators of aging, while senescence or cellular aging is one of the important denominators of aging.  

Factors 

The hallmarks of aging include genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication while the factors leading to senescence include oxidative damage, telomere shortening, DNA damage, mitochondrial DNA damage, tumor suppressors, and cell cycle inhibitors. 

Importance 

Moreover, aging is one of the major risk factors for cancer, cardiovascular disease, diabetes, and neurodegenerative disorders, while senescence causes aging and age-related diseases. 

Conclusion 

Aging is the biological process that leads to the progressive loss of physiological integrity. Environmental factors and time serve as the main factors which cause aging. Furthermore, there are 9-10 hallmarks which serve as denominators of aging. Senescence is one of them. It is the irreversible cell cycle arrest. Moreover, the factors leading to senescence include oxidative damage, telomere shortening, DNA damage, etc. Therefore, the main difference between aging and senescence is their contribution to cell death.   

References:

1. López-Otín, Carlos et al. “The hallmarks of aging.” Cell vol. 153,6 (2013): 1194-217. doi:10.1016/j.cell.2013.05.039
2. Dodig, Slavica et al. “Hallmarks of senescence and aging.” Biochemia medica vol. 29,3 (2019): 030501. doi:10.11613/BM.2019.030501

Image Courtesy:

1. “Alzheimer’s disease brain comparison” By derivative work: Garrondo SEVERESLICE_HIGH.JPG: ADEAR: “Alzheimer’s Disease Education and Referral Center, also a service of the National Institute on Aging.”PRECLINICALSLICE_HIGH.JPG (Public Domain) via Commons Wikimedia   
2. “Oregongrapeleaves” (Public Domain) via Commons Wikimedia