Wear and tear on the body increases with age

One of the hallmarks of aging is the wear and tear our bodies accumulate over time, specifically in our cells.

DNA

Changes in DNA and certain environmental exposures may lead to cell division errors or mutations. Cells can repair these genetic mutations, but their ability to do so declines with age — though scientists are unsure why.

"That's a $1 billion question," said Andrew Dillin, a professor of molecular and cell biology at the University of California, Berkeley. "All we know is that the efficiency goes down with age."

Over time, cells will not be able to correct mutated cells, and in some scenarios, there may be mutations in genes that suppress tumors, leading to the development of cancer.

Chromosomes

At the end of chromosomes are telomeres, which are special parts of the genome that stop chromosomes from unraveling. When telomeres get too short, cells will stop dividing.

Telomere shortening can prevent cells from replicating forever and becoming cancerous. However, when the same process occurs in stem cells, which help replenish skin, blood, and other tissues, you will likely experience physical signs of aging, such as gray hair and thinner, less elastic skin.

Epigenome

Epigenetics refers to chemical changes to the genome that affect which genes are turned on or off in a cell. Some epigenetic changes may occur naturally, while others are influenced by environmental factors.

Over time, the epigenetic mechanisms in our cells begin to degrade, and if this happens in too many cells, organ health and function can be negatively impacted. For example, epigenetic changes in heart cells can lead to thickened arteries or make it harder for the heart to respond positively to exercise.

According to Eric Verdin, the president of the Buck Institute on Aging, some anti-aging research has focused on epigenetic changes because they can be reversed more easily than DNA mutations or other changes.

Mitochondria

Mitochondria are responsible for energy production and are critical to cell health. Like other parts of cells, mitochondria become less efficient as we age, leading to less energy overall.

"If you're not generating enough energy, all of a sudden all of the other cellular processes are not going to function as efficiently," Verdin said. Damaged mitochondria may also cause inflammation, which is another aspect of aging that is associated with different chronic health conditions.

To improve your mitochondrial health as you age, experts recommend getting regular exercise.  

The body's disposal system is less effective over time

Another hallmark of aging is the reduced ability to dispose of faulty or malfunctioning cells in the body.

Disposing of bad cells

One way the body deals with malfunctioning cells is through a process called senescence. During this process, cells stop dividing and begin secreting inflammatory chemicals so the immune system knows to dispose of them.

Senescence is a normal part of cell turnover, but over time, the body's disposal system becomes less efficient, leading to a build-up of senescent cells and, in turn, inflammation.

"When we're young, normally our immune system is able to deal with the senescent cells," said Matthew Kaeberlein, CEO of the longevity company Optispan and the former director of the University of Washington Healthy Aging and Longevity Research Institute. "But as we get older, in part because of chronic inflammation, our immune system isn't able to do that anymore. So you get this accumulation of senescent cells, which then drives more damage, more inflammation, less immune function."

Currently, scientists are studying whether a class of drugs called senolytics may be able to enhance the disposal of senescent cells.  

Disposing of bad proteins

The body typically disposes of misfolded proteins, along with other malfunctioning parts of cells, through a process called "autophagy," which means "self-eating" in Greek. Like with other processes, autophagy usually declines with age.

"Autophagy is the process by which all these defective things in the cell are destroyed," said Venki Ramakrishnan, a biochemist and Nobel laureate. "And if you interfere with that mechanism, you get this pileup of, essentially, garbage in the cell, which itself causes stress and causes aging."

Researchers are currently studying certain drugs, including rapamycin, for their potential to increase the autophagy process. However, it's not clear how healthy people will be affected by the medication since it suppresses the immune response.

In general, experts say that experimental anti-aging treatments are not ready for broad use, but they are optimistic about future developments in the field. "So far, I would say the winds haven't been particularly quick, but there will be breakthroughs," said Dame Linda Partridge, a professorial research fellow in the division of biosciences at University College London.

For now, Partridge recommends people adopt healthy lifestyle habits, including exercise and good nutrition, if they want to age well. (Smith, New York Times, 3/20)

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