What causes human bodies to age? Here’s what scientists know about the biology behind growing old

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Japan elderly woman

Everything grows old. As you age, you may notice an extra wrinkle on your forehead or lower energy levels.

To find out what’s going on inside our bodies that causes these age-related changes and declines, he journal Cell assembled a group of researchers in 2013. That team, comprised of scientists studying different aspects of aging, reviewed all the existing literature on aging and wrote anl overview.

"The Hallmarks of Aging," as their paper was called, summed up everything that happens in our bodies biologically as we get old, and categorized those processes into nine"hallmarks."

They are:

biological hallmarks of aging infographic

Here’s what each of these hallmarks means and how they work.

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Errors appear in DNA.

One type of damage that occurs with aging is that errors start to appear in our DNA. When DNA is replicated, the code might not always be copied correctly — parts could get misspelled, and sections could be accidentally inserted or deleted. These errors are not always caught by the mechanisms in our bodies that repair DNA. 

The genetic code is a cell’s instruction manual, so as errors build up, they can wreck havoc. If the instructions become unclear or wrong over time, that could break down the cell and even make it turn cancerous. 

In old tissue, scientists have observed that many cells have a lot of accumulated genetic damage. If researchers can figure out how to improve the mechanism that repairs DNA, they could improve and possibly delay the aging process.

Gene expression goes awry.

Certain parts of your DNA are read and translated into physical traits. A group of proteins in your cells controls which genes ultimately get expressed. This process is called epigenetic moderation, and it’s what ensures your skin cells are different from brain cells, even though they use the same set of DNA. 

But as we age, the proteins bound to DNA become looser and less accurate, and genes start to get expressed when they shouldn’t be, or get silenced in error. This means some necessary proteins aren’t being made, and harmful, unnecessary proteins are. For example, if an inadvertent change results in the silencing of a gene that helps suppress tumors, cells could uncontrollably grow into cancer. 

Scientists have found that reversing these types of errors in gene expression can improve some neurological effects of aging in mice, such as memory impairment.

Telomeres may shorten.

Telomeres are protective caps at the ends of each strand of DNA. Some scientists have compared them to the plastic tips of shoelaces that keep them from fraying. 

Some research suggests that every time cells divide, the tips of the chromosome become shorter. When the telomeres are lost, chromosomes become unstable and all kinds of problems arise. The most notable is that chromosomes can’t replicate correctly, and end up fragmented or with extra parts that aren’t supposed to be there. These abnormalities usually kill cells or make them dangerous.

Scientists have figured out how to increase levels of telomerase – an enzyme that can extend the length of telomeres — in mice, and a study suggested that can extend mice’s lifespan. When they lowered levels of telomerase in mice, the mice lived shorter lives.

See the rest of the story at Business Insider

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