NCI Study Demonstrates That Cellular Defects in Premature Aging Disease are Reversible
Cells affected by Hutchinson-Gilford Progeria Syndrome (HGPS)
a disease associated with premature aging-- can be made healthy
again, according to findings by scientists at the National Cancer
Institute (NCI), part of the National Institutes of Health (NIH).
Using specially modified segments of DNA, NCI researchers Paola
Scaffidi, PhD, and Tom Misteli, PhD, reversed the abnormalities
seen in HGPS cells by correcting defects associated with the key
protein, lamin A. By demonstrating that HGPS cellular characteristics
are reversible, this study, appearing in Nature Medicine online
on March 6, 2005*, brings scientists one step closer to understanding
this devastating childhood disease and might provide insights into
the normal aging process.
HGPS is a rare inherited disease affecting about one in eight
million children. While appearing normal at birth, infants with
HGPS age rapidly after their first 18 months, and physical symptoms
include stunted growth, loss of hair and body fat, joint stiffness,
osteoporosis, and heart problems. The condition is fatal, with
heart disease being the leading killer, and affected children usually
die before they reach their late teens.
Less than two years ago, NIH-led researchers discovered that the
genetic basis for HGPS is a single mutation in the gene encoding
lamin A. Lamin A is a critical structural protein that acts as
the scaffolding which holds a cell’s nucleus together. Lamin
A is defective in HGPS cells because the mutation creates an aberrant
splice site in the lamin A gene; the aberrant splicing, or joining
the separate parts of the gene together, results in synthesis of
a truncated lamin protein. Without lamin A holding them together,
the nuclei of progeria cells become wrinkled and misshapen. In
addition, numerous other nuclear proteins show reduced expression.
“Our NCI team at the Center for Cancer Research in Bethesda
set out to ask whether these cellular changes associated with progeria
are permanent or reversible,” said Scaffidi. First, the investigators
added DNA encoding normal lamin A into cells taken from patients
affected with progeria, but observed that increased synthesis of
normal lamin A did not correct any of the progeria-associated defects.
In addition, they found that introduction of the mutant protein
into healthy human cells was sufficient to produce the disease
characteristics. “These results made it clear that in order
to achieve a potential therapeutic effect, we needed to completely
eliminate the mutant protein,” said Scaffidi.
The NCI researchers designed a chemically stable DNA oligonucleotide a
short DNA sequence that the cell wouldn’t be able to degrade
that would bind to the mutant splice site and prevent the splicing
machinery from cutting in the wrong place. “You can think
of it as a molecular Band-Aid®,” said Misteli. The researchers
inserted their oligonucleotides into the progeria cells and observed
that after four days almost all the mutant lamin A transcripts
had been eliminated and replaced with the properly spliced counterpart.
The oligonucleotide was highly specific to the mutated region and
did not cover-up other splicing locations. One week after correcting
the splicing defect, the mutant lamin A protein had been eliminated
and more than 90 percent of progeria cells were restored to normal;
visually, the nuclei lost their wrinkles and lobes and returned
to a natural ellipsoid shape, and the expression of other nuclear
proteins was also restored to normal levels.
“It’s amazing that we could take a cell that looked
about ready to die, and a few days later it was healthy and ready
to divide again,” said Misteli.
Misteli noted that these results demonstrate a proof-of-principle
that the cellular effects of progeria can be reversed, meaning
his laboratory’s method could be used some day in the future
as a therapeutic strategy. The fact that a progeria reversal can
be achieved in multiple cell types, and that the cells can return
to normal, independent of cell division, bolsters this possibility. “Some
tissues in our body do not divide,” Misteli pointed out. “So
demonstrating that we can rescue the normal phenotype without cell
division means this procedure could be effective in all tissues.” Misteli
and his group will also look more closely at healthy cells to determine
how similar progeria is to the normal aging process.
For more information about progeria, please visit the NHGRI Web
site at http://www.genome.gov/11007255.
For more information about cancer, please visit the NCI Web site
at http://www.cancer.gov or call NCI's Cancer Information Service
at 1-800-4-CANCER (1-800-422-6237).
* Paola Scaffidi and Tom Misteli, “Reversal of the cellular
phenotype in the premature aging disease Hutchinson-Gilford Progeria
Syndrome.” Nature Medicine, vol 11, no 4; April 2005.