[bksvol-discuss] OT: UCLA identifies enzyme linked to childhood blindness
- From: Cindy <popularplace@xxxxxxxxx>
- To: bksvol-discuss@xxxxxxxxxxxxx
- Date: Thu, 11 Aug 2005 23:27:47 -0700 (PDT)
I heard an quick item on the car radio, and when I
came home I looked it up. This may be of some interest
to some of you.
Cindy
UCLA researchers identify key enzyme linked to
childhood blindness
Findings could lead to gene therapy cure
In findings that could lead to curing some forms of
congenital blindness through gene therapy, researchers
at UCLA have discovered that RPE65, a gene missing in
infants born with the blinding disease Leber
congenital amaurosis, is also a key enzyme in the
visual cycle. The identity of this enzyme has long
been a mystery to scientists.
The study, "Rpe65 is the Retinoid Isomerase in Bovine
Retinal Pigment Epithelium," is published in the Aug.
12 issue of Cell magazine.
"We were amazed when we discovered the function for
Rpe65 -- and that Rpe65 is the retinoid isomerase. It
is a protein that all of us had known about for
years," said Dr. Gabriel Travis, professor of
ophthalmology and biological chemistry at UCLA's Jules
Stein Eye Institute and one of the researchers. "It's
like searching the world for a treasure, then
discovering it in your own back yard."
Leber congenital amaurosis is an inherited disease
that is believed to cause up to 20 percent of all
cases of childhood blindness. It is caused by
mutations in several different genes including RPE65.
An important characteristic of this disease is that
the light sensitive rod and cone cells remain intact
in the retinas of Leber patients for a long time.
"This suggests that replacement of RPE65 by gene
therapy should correct the blindness in these
children, as was observed in mice and dogs with RPE65
mutations," Travis said. "This is a major breakthrough
in understanding the visual cycle. It has
ramifications for several inherited blinding diseases
caused by mutations in visual cycle genes."
The newly identified isomerase enzyme plays a crucial
role in the regeneration of rhodopsin visual pigment
in the retina after light exposure. Rhodopsin contains
a light absorbing molecule called 11 cis
retinaldehyde, related to vitamin A, which is
converted upon light absorption to all trans
retinaldehyde in a process called photo bleaching.
This conversion is the first step in visual
perception.
Photo bleaching leaves the rhodopsin insensitive to
light until the all trans retinaldehyde is converted,
or "isomerized," back into 11 cis retinaldehyde, which
completes the visual cycle. Scientists have for two
decades been attempting to identify the retinoid
isomerase enzyme that catalyzes this regeneration of
11 cis retinaldehyde. Scientists have also been
stumped by the function of the Rpe65 protein
Working with Travis at the Jules Stein Eye Institute,
Dr. Minghao Jin, visiting assistant researcher in
ophthalmology, performed an expression screen in
cultured human cells, looking for a gene that caused
these cells to convert vitamin A into 11 cis retinol.
The researchers are now studying the effects on
retinoid isomerase activity of specific disease
causing mutations in the RPE65 gene, which should
provide more data on the cause of Leber congenital
amaurosis and on how the Rpe65 protein works. The
researchers are also examining the function of other
proteins that work closely with Rpe65. Mutations in
the genes for these interacting proteins are linked to
other forms of human blindness.
"These results settle the long standing mystery about
the identity of the retinoid isomerase," Travis said.
"Scientists have been searching for this enzyme for
almost 20 years. Our results also explain why finding
this enzyme has been so difficult, until now."
Other researchers on this project besides Travis and
Jin are Hui Sun, assistant professor of physiology at
UCLA, and Songhua Li and Walid Moghrabi, staff
research associates at the Jules Stein Eye Institute.
###
The National Eye Institute, the Foundation for
Fighting Blindness, and Research to Prevent Blindness
funded the study.
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