衰老的机理意义及治疗 The mechanism significance and treatment of aging

<p dir="ltr">The aging of an animal as a whole is caused by the senescence of stem cells within its tissues. However, the aging of human heart and brain tissues is also related to the senescence of cardiomyocytes and neurons. Therefore, age-related changes in immunity, endocrine function, the nervous system, and humoral factors ultimately result from cellular senescence and the reduction in cell number.</p><p dir="ltr">Cellular senescence is caused by the loss of multi-copy repetitive DNA—small nucleotide sequences located on chromosomes in the nucleus that indirectly control the rate of synthesis of general proteins (and also control the production of DNA inhibitors). This loss is referred to as the "cellular aging clock," and it leads to a decline in the overall rate of protein synthesis in the cell. These repetitive DNA sequences are lost during each cell division, and the number of copies lost is related to the activity of DNA synthesis: when DNA synthesis activity is high, fewer copies are lost, and vice versa. Caloric restriction extends lifespan primarily by reducing the synthesis of ATP, RNA, and cAMP—all of which inhibit DNA synthesis. Food nutrients, environmental factors, and other influences can also indirectly or directly inhibit DNA synthesis, thereby affecting lifespan. Normal somatic cells contain repair systems that can replenish these lost DNA sequences, but these systems are usually in a suppressed state. They are activated only in germ cells and cancer cells.</p><p dir="ltr">The roles of cellular senescence are: 1. Initiating cell differentiation; 2. Determining cell division; 3. Determining and initiating apoptosis; 4. Altering the expression rates of various genes; 5. Acting as a developmental program device and initiating developmental programs.</p><p dir="ltr">Activation of oncogenes can reverse the "cellular aging clock." Various factors can activate oncogenes, such as injury-induced regeneration of organs and tissues or viral infections. Administering drugs that do not damage DNA but can activate oncogenes in stages or as a single appropriate dose—especially in stem cells—can lead to a substantial rejuvenation of the individual. In addition, brief introductions to immune replacement therapy and cancer treatments are provided.</p>