Martin-Paul Agbaga, Ph.D
Oklahoma University Health Science Center - New Investigator
Project Title: Understanding the role of ELOVL4 protein and very long chain polyunsaturated fatty acids in retinal degeneration
Juvenile autosomal dominant Stargardt-like macular dystrophy (STGD3) is an inherited blinding disease in humans in which retina cells which allow for day time and fine vision are progressively destroyed. Since the retinal cells are non-replaceable once they die, patients progressively lose their central vision and eventually become blind. Three different forms of dominantly inherited mutations in a gene named ELOngation of Very Long chain fatty acids-4 (ELOVL4) has been associated with the disease. In other words, inheriting one bad copy of the gene from either parent is enough to cause the disease. From our studies and that of others, we have reasoned that there are two major possibilities that may be contributing to the death of the retinal cells in patients. In the first scenario, we know that the mutant protein loses its ability to be delivered to its proper place in cells and so it gets mislocalized. As a result, we think that, by being constantly delivered to and accumulating at the wrong “address” and generating toxic intermediate products that cannot be effectively cleared by the cells, the mutant protein
might be exerting cellular stress on the retinal cells. These eventually cause the retinal cells to die with a resultant loss of vision. We therefore seek to understand what role(s) the mutant protein plays in causing retinal cell death.
In the second scenario, we know that animals expressing one normal copy and one “bad” copy of
the ELOVL4 protein have reduced levels of a unique group very long chain polyunsaturated fatty acids (VLC-PUFA), of the omega-3 and -6 families of fatty acids. These fatty acids are found in tissues which express ELOVL4: the retina, testis, sperm, and brain. We have shown that the wild type ELOVL4 protein is involved in biosynthesis of VLC-PUFA. We believe that VLC-PUFA together with other omega 3 and 6 fatty acids play very important roles in the retina, hence their loss/reduction in the disease situation causing the cells to die. We reason that this loss/reduction in VLC-PUFA due to the misrouting of both mutant and the wild type protein from the site where these fatty acids are made and where the normal ELOVL4 protein are normally delivered, causes the photoreceptor cells to die. This suggests that, if indeed loss of VLC-PUFA is the cause of retinal degeneration in STGD3 patients, then dietary feeding or other innovative ways to specifically deliver VLC-PUFA to the retina of patients will provide some therapeutic benefits and prevent or delay death of the retina cells.
By finding answers to the two scenarios discussed above, we believe that we will have a better
understanding of the details of WHY and HOW the retina cells are destroyed so that we will be able to better define and design effective therapeutic strategies to prevent or at least delay the onset of retinal cell death in STGD3 patients.
Novrouz Akhmedov, PhD
UCLA - Visionary
Project title: "Studies on 7R, a novel protein that when mutated causes autosomal recessive retinitis pigmentosa"
Our research is focused on the identification of genes that when mutated cause retinal degenerations in animal models and humans. One gene recently isolated in our laboratory produces a novel retinal protein, 7R. This protein appears to be involved in the development of the retina and in the formation of the outer segment of cone photoreceptors. We have discovered that in a family with autosomal recessive retinitis pigmentosa (arRP), only the members that have inherited from each parent an allele with a mutated 7R are affected with the disease; those members with only one mutated 7R allele are carriers and do not have retinitis pigmentosa. Our studies on 7R will not only increase our understanding of this protein’s function in the retina, but may also uncover new treatment possibilities for retinitis pigmentosa and other related degenerative diseases.
Joseph Carroll, PhD
Medical College of Wisconsin - Visionary
Project Title: "Advanced Retinal Imaging and Improving the Success of Gene Therapy"
The objective of Dr. Carroll’s project is to characterize how disruptions in the cone cells of the retina affect visual function. In order for gene therapy to work (whether it be for achromatopsia, LCA, colorblindness, RP or other retinal disease), the cell type that you are trying to functionally rescue in a specific retinal disease must be structurally present. In order for us to evaluate eligibility for, or responses to a given therapy, we must be able to measure the function, or altered function of the targeted cells. Using achromatopsia as a model, we are developing a clearer understanding of the photoreceptor mosaic in normal and diseased retinas and across populations sharing common genetic mutations affecting the visual system. Such an understanding will allow clinicians to predict who might be the best candidates for a given therapy and simultaneously, which regions within the retinas of these candidates might be most receptive to therapy.
Sai Hemanth Chavala, MD
The University of North Carolina at Chapel Hill - New Investigator
Project Title: "Role of SOX2 and PAX6 in adult ciliary body progenitor"
Loss of central vision significantly impairs the quality of life of patients suffering from retinal degeneration, and renders some patients unable to function independently or enjoy their surroundings. The common denominator of retinal degeneration is the loss of functioning retinal neurons. These are cells that comprise the retina, and are responsible for processing light rays into visual information that is relayed to the brain, leading to the perception of sight. When retinal neurons are damaged by injury or disease, they are no longer capable of processing visual information. Loss of vision can result from direct damage to retinal neurons or from an inadequately functioning supporting pigmented layer underneath the retina, called the retinal pigment epithelium.
Stem/progenitor cells provide a unique and exciting strategy for replacing damaged retinal cells or retinal pigment epithelial cells in almost all forms of retinal degeneration. In general, stem/progenitor cells are cells that possess the capacity to make new cells that replace damaged tissue as a result of injury or disease. There are several sources of stem cells that can be used for this purpose; some are derived from embryos, while others are derived from the organs of adults. Adult organ-specific stem cells are attractive because these stem cells are thought to be restricted to creating progeny that are restricted to a specific organ, unlike embryonic stem cells that possess the capacity to produce a wide variety of cells from different organs. Controlling the cellular diversity that results from embryonic stem cells has been difficult, and tumors consisting of various cell types have been reported from the use of embryonic stem cells. Recently, a progenitor cell population has been discovered in the ciliary body, a region adjacent to the retina near the lens of the adult eye. This region is readily accessible using current surgical techniques, and warrants further study as a tool to replace damaged retinal neurons and retinal pigment epithelial cells. The use of patient specific retinal progenitor cells (cells derived from the patient’s own eye) provides an exciting opportunity to restore visual function for patients who currently have few or no options.
Shiming Chen, PhD
Washington University - Visionary
Project Title: rAAV Gene Therapy in Mouse Models of CRX-Associated Retinal Degenerative Diseases
The goal of this proposal is to develop safe, effective therapies for retinal degenerative diseases resulting from mutations in the transcription factor CRX. Human CRX mutations are linked to blinding diseases: retinitis pigmentosa, cone-rod dystrophy and Leber’s congenital amaurosis. To date, little has been done to develop therapies for diseases caused by genetic defects in retinal transcription factors. These factors coordinate the expression of sets of genes that work together to carry out a cell’s functions, like converting light to a neural signal in photoreceptors (rods and cones). Mutations in transcription factors have a wide-spread effect because these factors interact with each other and other proteins in a synergistic manner. Changing the function of one transcription factor affects a much larger group of proteins, creating potentially devastating effects on gene expression. The complexity of these changes makes designing drug-based approaches exceedingly difficult. We anticipate that the best therapy strategy is to supply a corrected copy of the CRX gene to the affected cells. For this reason we have chosen gene therapy as the best approach. Gene therapy uses a modified non-replicating virus to deliver intact copies of genes to cells with genetic defects. Often delivering a single gene is sufficient to completely restore the function of the cell. In animal models of retinal diseases, treatment strategies using the recombinant adeno-associated virus (rAAV) vector have both improved the vision of visually impaired animals and restored vision to previously blind animals.
Human clinical trials have also shown that rAAV gene therapy is both safe and effective, establishing rAAVmediated gene therapy as a promising treatment for retinal degenerative diseases. Therapy development for transcription factor-related retinal diseases has been delayed because of the lack of good animal models to test potential treatments and the unique obstacles caused by transcription factors’ complex interactions. CRX exerts the most central function of the disease-causing retinal transcription factors, as it is required for the expression of many genes in both rods and cones. We have developed two new mutant mouse models (R90W and E168d2) that replicate CRX-associated human disease much more closely than the previous Crx knock-out (Crx-/-) model. For the first time, these models will permit the evaluation of gene therapy in treating this important class of blinding diseases.
Daniel Chung, DO, MA
University of Pennsylvania - Visionary
Project title: "In Utero Gene Therapy for Inherited Retinal Degenerations"
As many forms of retinal degeneration have an early onset, some at infancy and even before birth, the concept of early intervention gene therapy may have a beneficial impact. This study proposes to use cutting edge technology to delivery genes to mouse models of retinitis pigmentosa at an embryonic level, in hope of having greater ability in decrease, stop or reverse the progression of the disease. Although, the concept of human fetal gene therapy is of the distant future, the results of this study, may give better understanding and foundation for the earlier treatment of children with retinal degenerative disease with gene therapy at a neonatal level.
This study will help us better understand the implications in intervening early in the retinal development of inherited retinal degeneration retinas with gene therapy. It will give clues as to the best time to intervene, and if earlier intervention is better. It is anticipated that retinal recovery will be at least to the level of gene therapy conducted at later time-points and hope is for greater visual stability and recovery.
Therese Cronin, PhD
University of Pennsylvania - Visionary
Project Title: "Restoring function to degenerated retinas by gene therapy using virally encoded light-responsive molecules"
Blindness frequently results from degeneration and disease of the light-sensitive tissue at the back of the eye called the retina. This is true for the spectrum of pathologies classed as Retinitis Pigmentosa as well as for Age-Related Macular Degeneration. Many retinal therapies focus on preventing or stemming the progression of these blinding diseases. There are fewer options available to restore sight to patients for whom the symptoms are advanced and significant loss of vision has already occurred. This project is therefore concerned with the therapeutic use of light-sensing proteins adapted for the retina. These molecules are of increasing interest as part of the field of optokinetic technologies. Significant international research efforts have gone into engineering such proteins so that they may restore light sensitivity to the remaining cells in the degenerated retina. The efficient delivery of these “molecular prosthetics” is now necessary in order to test their efficacy in vivo; however retinal delivery has proven a major bottleneck to the project. Our goal is to overcome this obstacle by the development of retinal targeted viral delivery tools.
Testing viral-mediated transfer of light-sensitive genes to the inner retina of non-human primates will be the first step in developing a viable treatment strategy that could be applied to humans with end-stage retinal degeneration. Given the current state of the art in retinal gene transfer, which has so far been found to be safe and efficacious in at least 18 patients, it is timely to explore the options for gene-based restoration of visual function in cases of advanced blindness.
We anticipate that by overcoming the obstacle of targeted delivery to intermediate cell layers of the retina, we can accelerate the effort to bring these optokinetic molecules such as Channelrhodopsin-2 to the point of clinical testing.
Marina Gorbatyuk, PhD
University of North Texas - Visionary
Project Title: "Anti-apoptotic Gene Therapy for ADRP rat model"
This project is focused on the elucidation of the roles of pro-apoptotic proteins CHOP/GADD153 and caspase-7 in provoking apoptosis in autosomal dominant retinitis pigmentosa (ADRP) photoreceptors affected by mutated rhodopsin (RHO) and design anti-apoptotic gene therapy for ADRP rat model. Retinitis pigmentosa (RP) is the most common inherited form of blindness, affecting about 1 in every 4000 people in all ethnic groups worldwide. RP can be transmitted either as an autosomal dominant (ADRP), autosomal recessive (ARRP), or X-linked trait. More than 100 mutations in rhodopsin account for approximately 30% of ADRP cases with varying severity of visual impairment. Misfolded opsin causes endoplasmic reticulum (ER) stress by interfering with the trafficking of wild-type rhodopsin, accumulating in the ER and stimulating a signal transduction cascade in ADRP photoreceptors known as the Unfolded Protein Response (UPR). If unchecked, this pathway triggers photoreceptor death through activation of apoptosis. Although supplementation with vitamin A may be beneficial in some cases, currently, there is no effective pharmacological therapy for ADRP. Therefore, the major objective of this proposal is to determine whether gene therapy based on the blockage of the ER stress associated apoptosis is a viable treatment.
Michael A. Grassi, MD
University of Chicago - Visionary
Project title: "Role of the Extrinsic Apoptotic Pathway in Retinitis Pigmentosa (RP)"
Photoreceptors are the light sensing cells of the eyes. They are composed of the rods (dim light) and cones (color and fine vision). RP is a disease that primarily causes loss of the rods. It is the loss of cones, though, that is so devastating from a functional standpoint to patients with RP. Cones die secondarily from a bystander effect due to changes in the cellular microenvironment created by the injured and dying rods.
We anticipate increasing the understanding of external death signaling between rods and cones in RP. We hope to use this knowledge to increase the survival of the cones thereby allowing patients with this disease to maintain functional vision longer.
Stephanie A. Hagstrom, Ph.D.
Cleveland Clinic - Visionary
Project Title: "The Role of Tulp1 in Photoreceptor Protein Trafficking"
Retinitis pigmentosa (RP) incorporates a large number of inherited retinal disorders characterized by photoreceptor degeneration. RP is genetically and phenotypically heterogeneous, affecting over 1 million individuals worldwide. Mutations in a gene called TULP1 underlie an early-onset and severe form of autosomal recessive RP. Tulp1 is a protein exclusive to photoreceptor cells, and although the function of Tulp1 remains elusive, there is evidence from the murine model lacking Tulp1 that it plays a role in intracellular protein movement in multiple compartments of the photoreceptor. In tulp1-/- mice, prior to photoreceptor degeneration, rod and cone opsins are mislocalized, and rhodopsin-bearing extracellular vesicles accumulate around the ellipsoid region of the inner segment (IS), indicating that Tulp1 is necessary for the transport of proteins to the outer segment (OS). These mice also have a synaptic malformation that precedes photoreceptor degeneration and most likely interferes with the proper development of post-receptoral neurons. The absence of Tulp1 results in abnormalities that affect structure and function in multiple retinal sites, as well as causing distinct abnormalities in separate photoreceptor compartments. This suggests that it either performs a general role throughout the photoreceptor or participates in multiple distinct pathways. Based on our published work, the central hypothesis of this proposal is that Tulp1 is a component of the molecular machinery involved in the vesicular movement of proteins in the photoreceptor cell.
At the successful completion of this work, we will position Tulp1 in a functional context and define its mechanism of action. Our results will provide insight into the functional organization of photoreceptor protein transport pathways, as well as insight into the perturbation of retinal function associated with TULP1 mutations. Finally, this project has potential for significantly impacting an important aspect of photoreceptor biology relevant to human retinal disease.