Sunday, February 5, 2012

Mechanism explains why cells age and cause disease

Cells have a certain life span. After a while, they stop dividing and that eventually means our life comes to an end, if we are fortunate enough to live long enough to let the ageing process run its course. A study performed on nerve cells in rats by the Salk Institute for Biological Studies gives an explanation about why cells age, aside from existing theories. Apparently, cells contain proteins that are as old as the organism itself. It means they are not renewed, while most proteins renew every two days tops. These 'extremely long lived proteins' (ELLP) may explain why our cells age, as they suffer damage over time.

ELLP are present on the edge of the cell's core, which is called the nucleus. Cells store genetic material in the form of chromosomes there, which means it needs to be protected. Because certain molecules need to be transported in and out of the nucleus, there is a 'border patrol' controlling what is being transported. This way, instructions from the DNA that need to be made into proteins can be transported out of the nucleus, while damaging chemicals stay out, for example. ELLP are tasked to control what goes in and out, and are so-called transporter channels.
The nucleus (blue) bordered by ELLP (green)
As said, most proteins have are being readily replenished. Our cells need billions of proteins throughout it's lifetime, but some of the ELLP are only issued once. That makes these proteins and their function susceptible for damage. According to Salk Institute, this is exactly what happens in rat nerve cells. Certain chemicals affect the structure of the ELLP, which means their ability to allow the right molecules to pass in and out of the nucleus declines. Eventually that leads to harmful chemicals entering the nucleus, damaging the DNA.

Because nerve cells themselves are also barely replaced by the body, the decline induced by damaged ELLP will eventually lead to degeneration of brain functions. This is also what we see in older people: elderly frequently have gaps in their brain, resulting from damaged nerve cells that have been cleared away. It impairs neurological functions and generally adds to the ageing process. It could be a cause of age-related dementia or other neurodegenerative diseases commonly found in the elderly.

The study performed by Salk Institute for Biological Studies sheds light on how our brains deteriorate with age. It appears that ELLP play an important role in the ageing process and cognitive decline. If we better understand how these long-lived proteins are damaged over time, we may be able to do something about it, and increase our life span. 

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