X-Message-Number: 13262
From: Brent Thomas <>
Subject: possible genetic intervention for ageing
Date: Thu, 17 Feb 2000 09:45:07 -0500

taken from -- http://news.excite.com/news/r/000216/14/science-science-aging

LONDON (Reuters) - U.S. scientists have uncovered new information about a
gene in yeast that they
  think could one day be used to increase the lifespan of humans.

  The gene is called Silent Information Regulator, or SIR2.

  In yeast cells it controls longevity by silencing, or turning off, whole
sections of the yeast genome.

  Leonard Guarente and scientists at the Massachusetts Institute of
Technology (MIT) have discovered
  how SIR2 works and are trying to determine if it could extend the lives of
animals and possibly humans.

  "It is a conserve gene. We have it, mice have it. It's ubiquitous. We know
in yeast it can extend lifespan.
  We know it has this activity which connects metabolic rate to genome
silencing and in yeast cells
  promotes longevity," Guarente said in a telephone interview Wednesday.

  "The connection between aging and metabolism rate is universal. For many
years we've known that if you
  restrict calories you slow metabolic rate and the organism lives longer."

  In a report in the science journal Nature, the researchers described how
they discovered that organisms
  such as yeast which have an extra copy of the SIR2 gene live longer. But
if yeast has no SIR2 gene the
  cells' life span decreases.

  They also found that SIR2 needs another co-enzyme, called NAD, which is
intimately associated with the
  metabolic rate of cells, to work.

  "We think it is a reasonable inference that SIR2 is coupled to NAD so that
it senses the metabolic rate of
  cells and then decides how much silencing to impose," Guarente added.

  If NAD is too high it comes in and silences more.


  Previous studies have shown that the life spans of yeast, earthworms, mice
and possibly primates can be
  extended by restricting calories to 70 percent of normal levels.

  The MIT researchers suspect that if an organism is starved for calories,
the NAD level may go up. More
  NAD means activating SIR2, which silences sections of the genome and
increases life span.

  As yeast cells age some of their genetic material falls off the chromosome
and accumulates in the cell,
  eventually causing it to die. SIR2 seems to prevent this by silencing
parts of the genome.

  The researchers said SIR2 is also probably involved in silencing mouse
cells in response to metabolism.

  "If you give yeast more SIR2 genes they live longer. Will that be true in
animals? That's the acid test. If it
  is true, it's exciting because it suggests we will be able to intervene in
this (aging) process," he added.

  When the scientists gave the yeast one extra copy of the gene it extended
their normal lifespan by about
  40-50 percent.

  "All investigations led us to this gene," said Guarente. "If we can keep
SIR2 active for longer, we may
  slow down aging." 

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