Aging and age-related diseases

Aging is caused by the random changes in molecular, cellular, and organismal structures and functions over time, as well as their interactions with the environment. Aging increases the likelihood of death. Aging is a stochastic process that does not evolve, and therefore, it does not involve genetic regulation, and it cannot be directly controlled or intervened with.

The process of aging is often accompanied by various symptoms such as elevated blood sugar and blood pressure, decreased organ function, and reduced immune function. Sometimes, these symptoms can escalate into diseases such as diabetes, hypertension, and osteoporosis. Therefore, some scientists consider aging as a type of disease.

Unlike diseases, aging occurs in all individuals. From the previous definition, we can infer that aging is a cumulative effect of various random factors acting over time and cannot be summarized as a specific disease.

Thanks to improvements in hygiene and medical conditions, human lifespans have greatly increased in the past century. However, the reason for increased longevity is not that people have resisted the march of aging but that there are more treatments available for age-related diseases.

The discovery of longevity genes and aging genes is an exciting development, but it has also led some to mistakenly believe that there is a switch in our bodies that controls aging, and that simply turning it off could lead to eternal youth. In reality, these genes are not the causes of longevity or aging, and they cannot be easily manipulated to control the human body.

Aging can indirectly lead to the development of many age-related diseases. Most human diseases appear to be associated with the aging process, and the loss of normal, age-related physiological functions can transform into manifest diseases.

Cellular aging is an internal cause of human aging. Aging cells exit the cell cycle, cease dividing, and are not directly cleared from the body but accumulate in tissues and organs.

Aging cells contain a significant amount of damaged DNA, leading to cellular dysfunction. Additionally, they secrete a large number of inflammatory factors, chemokines, and growth factors into the surrounding environment, continuously stimulating neighboring cells. The accumulation of these changes results in the gradual aging of specific organs or physiological systems. The aging of organs or physiological systems inevitably leads to a decline in overall bodily functions, reduced immune function, and decreased adaptability to environmental changes, ultimately resulting in age-related diseases.

Therefore, aging cells are the culprits behind the development of most age-related diseases. Traces of aging cells can be found in many common age-related diseases in humans.

Atherosclerosis is one of the most basic age-related diseases. In atherosclerosis, lipids in the blood deposit on the inner walls of blood vessels, forming plaques that can lead to severe conditions such as stroke, heart attack, and congestive heart failure. Scientists have found numerous aging cells in the initial lesion sites on the inner walls of blood vessels in mouse models of atherosclerosis. These aging cells produce a large number of factors that promote the development of atherosclerosis. Removing these aging cells from these locations can alleviate the progression of the disease.

In osteoarthritis, scientists have also found aging cells in joint cartilage and synovium, and their accumulation with age or in response to damage can lead to arthritic changes. Clearing these aging cells from these locations can alleviate pain and promote cartilage repair.

The aging of neutrophils and macrophages in the human immune system can lead to reduced phagocytic capacity, while the aging of NK cells can reduce tumor antigen recognition and pathogen immune responses. The thymus, located behind the sternum, is also affected by the accumulation of aging cells, leading to thymic atrophy, which hinders the development, differentiation, and maturation of T cells. Therefore, older individuals are more susceptible to infections and inflammation.

Neurodegenerative diseases such as Parkinson's and Alzheimer's are directly related to the aging of the brain. Aging cells in the brain impair its ability to clear damaged proteins, and the accumulation of neurotoxic complexes such as amyloid plaques and tangled neurofibrillary fibers in the brain can lead to some individuals transitioning from normal aging to overt disease.

Anti-aging research not only seeks to change the mechanisms underlying aging but also aims to improve the health of elderly people by treating age-related diseases, thereby extending the "healthy" lifespan of humans. This is a major direction in anti-aging research, allowing people to live as healthy as possible within their limited lifespan and then considering extending their overall lifespan, achieving healthy longevity.