Theories of Aging PDF

Theories of aging BELINDA DUODU Introduction Aging can be defined as the time- related deterioration of the physiological functions necessary for survival and fertility Aging process is the process of growing old or developing the appearance and characteristics of old age Each theory of a...

Theories of aging BELINDA DUODU Introduction Aging can be defined as the time- related deterioration of the physiological functions necessary for survival and fertility Aging process is the process of growing old or developing the appearance and characteristics of old age Each theory of aging attempts to provide a framework in which to understand aging from different perspectives The following will be discussed: Genetic Non- genetic cellular theories Physiological theories of aging Genetic theories of aging Your DNA may predict more about you than the way you look. According to the genetic theory of aging, your genes (as well as mutations in those genes) are responsible for how long an individual will live. Our genes are contained in our DNA which is present in the nucleus (inner area) of each cell in our bodies. We each have 46 chromosomes making up our DNA, 23 of which come from our mothers and 23 which come from our fathers. Of these, 44 are autosomes, and two are the sex chromosomes, which determine if we are to be male or female.  Within these chromosomes lie our genes, our genetic blueprint responsible for carrying the information for every process which will take place in our cells. Our genes can be envisioned as a series of letters that make up words and sentences of instructions. These words and sentences code for the manufacturing of proteins that control every cellular process. If any of these genes are damaged, for example, by a mutation that alters the series of "letters and words" in the instructions, an abnormal protein may be manufactured, which in turn, performs a defective function. If a mutation occurs in proteins that regulate the growth of a cell, cancer may result. If these genes are mutated from birth, various hereditary syndromes may occur  Genetic theories of aging seek to explain the biological mechanisms underlying the aging process and why organisms age over time. These theories suggest that genetic factors play a significant role in determining the rate and characteristics of aging. The genetic theory of aging states that lifespan is largely determined by the genes we inherit. According to the theory, our longevity is primarily determined at the moment of conception and is largely reliant on our parents and their genes.  People whose parents and ancestors have lived longer, tend to live longer and vice versa. Genetics alone are not the sole cause of aging. Studies looking at identical twins reveal that there is clearly something else going on; identical twins who have identical genes do not always live an identical number of years. Some genes are beneficial and enhance longevity. E.g., the gene that helps a person metabolize cholesterol would reduce a person's risk of heart disease.  The basis behind this theory is that segments of DNA that occur at the end of chromosomes, called telomeres, determine the maximum lifespan of a cell. Telomeres are pieces of "junk" DNA at the end of chromosomes which become shorter every time a cell divides. These telomeres become shorter and shorter and eventually, the cells cannot divide without losing important pieces of DNA How to reduce genetic aging of cells Exercise - Studies have found that physical activity not only helps your heart and lung function well, but exercise lengthens telomeres. Eat a healthy diet – A diet high in fruits and vegetables is associated with greater telomerase activity (in effect, less shortening of the telomeres in your cells). A diet high in omega-3-fatty acids is associated with longer telomeres but a diet high in omega-6-fatty acids is the opposite and associated with shorter telomeres. In addition, soda pop intake is linked with shorter telomeres.  Reduce stress Avoid carcinogens Maintain a healthy weight - Not only is obesity linked with some of the genetic mechanisms associated with aging noted above (such as increased shortening of telomeres), but repeated studies have found longevity benefits associated with caloric restriction. Non- genetic cellular theories of aging Non-genetic cellular theories of aging focus on the role of cellular processes and mechanisms that contribute to aging, independent of genetic factors. These theories highlight the cumulative effects of various cellular changes and damage over time. Here are some key non-genetic cellular theories of aging: Stochastic theories of aging According to this theory, the body ages as a result of random assaults from both the internal and external environments. These theories which are sometimes wear and tear theories of aging, compare the human body to a machine that simply wears out as a result of constant use, with the added accumulation of cellular insults and injuries. In one such theory for eg, it is thought that as cells age, they have a harder time disposing off waste. Accumulation of fatty deposits in these cells e.g. blood vessels takes up space and eventually slow down the normal process.  A more popular stochastic theory involves the action of pieces of molecules called free radicals (unstable molecules produced during cellular metabolism) In the course of normal use of oxygen for virtually every cellular process, small, highly charged, unpaired electrons are left. These free radicals react with other chemical compounds in the cell and may interrupt normal cell functioning. Normally the cell has repair mechanism to reduce the damage done by free radicals. Great free radical damage is noted after major injuries such as heart attack or exposure to radiation  Damage might be done to DNA in the genes. E.g. it is known that the ultraviolet light in sunshine can damage the DNA in skin cells. When the genes in a cell are damaged, the cell either repair itself or dies and is replaced by other cells. In older people there is less efficient repair and damage remains. This decline in self- repair capacity is aging Wear and tear seems to affect tissues and systems as well Limitation of the stochastic theories Limitation- the stochastic theories do not explain why the body’s internal “repair shop” functions remarkably well for a while to repair the damage due to random environmental assaults but then stops working They do not also explain why exercise, a potential form of wear and tear has beneficial rather than negative effects Programmed or clock theories of aging These theories suggest that the programmed actions of specific inherited genes determine aging. Biological clocks are associated with programmed aging (there is some kind of built- in timer or clock that is set to go off at a certain time). This clock may be located in each cell or it may be an external pacemaker, perhaps in the brain  Another clock theory suggests that there is some sort of pacemaker or timer housed in the hypothalamus and also in the pituitary gland. The pituitary gland releases a hormone shortly after puberty that begins the process of decline at a programmed rate Biological clocks in humans appear to control the female menstrual cycle which begins around age 12 and ends around age 50  A biologic clock also appears to control the immune system which gains strength until age 20 and then gradually weakens. Some theories suggest that this decline in immune function is linked to many age- related conditions including susceptibility to cancer and infections like influenza, pneumonia as well as to alteration in the wall of the blood vessels, which leads to arteriosclerosis Physiological theories of aging Physiological theories of aging focus on understanding how changes in physiological processes contribute to the aging process. These theories explore the alterations that occur in various organ systems and biological functions over time. Here are some key physiological theories of aging:  Mitochondrial theory: Mitochondria become less efficient and generate more free radicals as one ages. Hormonal changes  Metabolic Theory: The metabolic theory of aging focuses on the role of metabolism in the aging process. Changes in metabolic pathways, including alterations in nutrient sensing, mitochondrial function, and cellular energy production, are thought to influence aging-related processes such as cellular senescence, inflammation, and oxidative stress.  Caloric Restriction: Caloric restriction, reducing caloric intake without malnutrition, has been shown to extend lifespan and delay the onset of age-related diseases in various organisms. The physiological mechanisms underlying the effects of caloric restriction on aging are complex and may involve alterations in metabolic signaling pathways, cellular stress responses, and energy metabolism.  These physiological theories of aging provide insights into the complex biological processes that contribute to aging-related changes in tissues and organ systems. Understanding these mechanisms may lead to the development of interventions to promote healthy aging and prevent age-related diseases. References Goldsmith, T.C. Evolution of aging theories: why modern programmed aging concepts are transforming medical research. Biochemistry (Misc) 2016 Dec; 81(12)1406- 1412 Jin K. Modern biological theories of aging. Aging Dis. 2010;1(2):72-74. Ishikawa N, Nakamura K, Izumiyama-shimomura N, et al. Changes of tIshikawa N, Nakamura K, Izumiyama-shimomura N, et al. Changes of telomere status with aging: An update. Geriatr Gerontol Int. 2016;16 Suppl 1:30-42. doi:10.1111/ggi.12772 Salvestrini V, Sell C, Lorenzini A. Obesity may accelerate the aging process. Front Endocrinol (Lausanne). 2019;10:266. doi:10.3389/fendo.2019.00266 Telomere status with aging: An update. Geriatr Gerontol Int. 2016;16 Suppl 1:30-42. doi:10.1111/ggi.12772 IsIshikawa N, Nakamura K, Izumiyama-shimomura N, et al. Changes of telomere status with aging: An update. Geriatr Gerontol Int. 2016;16 Suppl 1:30-42. doi:10.1111/ggi.12772 hikawa N, Nakamura K, Izumiyama-shimomura N, et al. Changes of telomere status with aging: An update. Geriatr Gerontol Int. 2016;16 Suppl 1:30-42. doi:10.1111/ggi.12772