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Director: Stephanie A. Hagstrom, Ph.D.
Department of Ophthalmic Research
Cole Eye Institute
9500 Euclid Avenue, i32
Office telephone: 216/ 445-4133
Fax: 216/ 445-3670
Email: hagstrs@ccf.org
From left,
Quansheng Xi, Ph.D., Gayle T. Pauer, Stephanie A. Hagstrom, Ph.D.
Not pictured:
Andrea Crabb, Alison Szabo and Alyssa Wiener
Goals and
projects of Hagstrom Lab:
Genetic Analysis of Inherited Retinal Diseases
One of the main objectives of our
lab is to identify and analyze genes responsible for inherited retinal
degenerations such as retinitis pigmentosa, Leber congenital amaurosis and
juvenile and age-related forms of macular degeneration. These objectives are
met through a candidate gene approach involving the collection of DNA samples
from patients with inherited retinal diseases, the selection of candidate genes
based on a well-established set of criteria and large-scale mutation screening
of the DNA samples using high-throughput, semi-automated molecular genetic
techniques.
Retinitis pigmentosa (RP) is a
genetically and phenotypically heterogeneous family of inherited retinal
diseases. These diseases are characterized by progressive night blindness and
peripheral visual loss, which then progresses to loss of central vision.
Similar to RP, Leber congenital amaurosis (LCA) is the earliest and most severe
form of inherited photoreceptor degeneration and is usually recognized at birth
or shortly after. Both disorders feature attenuated retinal vessels, retinal
pigmentary deposits and a reduced or nondetectable electroretinogram.
Macular degeneration is a separate heterogeneous
group of retinal disorders characterized by progressive central vision loss. Age-related
macular degeneration (AMD), the most common form of the disease, is the leading
cause of visual impairment in the United States and in many developed
countries. Based on clinical evaluation, AMD may be divided into two major
subtypes. Approximately 80% of patients have atrophic or “dry” AMD, which is
associated with drusen within or under the retinal pigment epithelium (RPE),
irregularities in RPE pigmentation, and geographic atrophy of the posterior
pole. The remaining 20% of AMD patients have the “wet” form, characterized by
choroidal neovascularization (CNV) and/or RPE detachment. The most marked
visual losses are associated with the presence of geographic atrophy or CNV.
Stargardt disease is the most common form of juvenile macular dystrophy and
shares many important clinical and histological features with AMD.
To date, mutations in more than 85
genes have been identified in hereditary retinal degeneration, including those
diseases listed above, and it is estimated that an additional 50 disease-causing
genes remain to be identified (www.sph.uth.tmc.edu/Retnet). The numerous genes
and gene defects that have been identified suggest that many different
mechanisms may lead to a common end point, photoreceptor cell death, and
motivate our plan to continue to screen candidate genes causing inherited
retinal degenerations.
Most importantly, the
identification of defective retinal genes has a number of potential clinical
benefits for patients:
1) It can have prognostic value
since there are correlations between specific mutations and severity of visual
loss;
2) It can improve genetic
counseling by refining the diagnosis to include the specific genetic defect,
allowing specific molecular diagnostic assays to be applied to the patient’s
family;
3) It can have implications for
therapy, since cataloguing the set of gene defects that cause retinal
degeneration will help in understanding the pathogenic disease mechanisms. It
is through this knowledge that agents might be developed that slow, stop or
reverse these blinding diseases.
The Function of TULP1 in Normal Photoreceptors and in
Photoreceptor Degeneration.
The long-term objectives of this
project are to explore the physiologic properties of the TULP1 gene product in
the retina and define the underlying pathogenic mechanism responsible for
photoreceptor degeneration associated with TULP1 mutations. We
previously identified mutations in TULP1 that cause a form of autosomal
recessive RP, a group of progressive retinal degenerations leading to blindness.
TULP1 is a member of a family of
four proteins named TULPs for tubby-like proteins, defined by the highly
conserved C-terminal half of their primary sequences. This protein family
includes TUB, TULP1, TULP2 and TULP3, all of which have very different N-termini.
Database searches do not reveal any significant homology with known proteins or
functional motifs. Their physiological functions are unknown but two (TULP1 and
TUB) have been linked to photoreceptor degeneration.
We have begun to explore the role of TULP1 in the retina by analyzing
the tissue distribution of the protein in normal mice and the photoreceptor
disease phenotype in tulp1 knockout mice. We determined that the Tulp1 protein is found
exclusively in the photoreceptors, localizing predominantly in the inner
segments and connecting cilium. In addition, tulp1 -/- mice develop
early-onset, progressive photoreceptor degeneration with involvement of both
rods and cones. At an early age, the rod and cone opsins, normally targeted to
the outer segment, were aberrantly localized to the plasma membranes of inner
segments, perinuclear cytoplasm and synaptic regions. At the same age, an
abnormal accumulation of rhodopsin-bearing extracellular vesicles was found
surrounding the ellipsoid region of the inner segments.
Based upon our data, we hypothesize that TULP1 is involved in the
polarized transport of nascent opsin from its site of synthesis in the inner
segment to its final destination in the outer segment. We are testing this
hypothesis using several different approaches. We are using a proteomic
approach to identify cellular proteins that interact with Tulp1 and a cell
biological approach to determine the subcellular localization of wild-type
Tulp1 and mutant versions of Tulp1.
Lab staff members:
Stephanie A. Hagstrom, Ph.D. –
Director
Quansheng Xi, Ph.D. – Postdoctoral
Fellow
Gayle T. Pauer – Lab Manager
Andrea Crabb – Student
Alison Szabo – Student
Alyssa Wiener - Student
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