Grants Approved 2008 - 2009
Rod Bremner - Estate of Olga VariolloUniversity Health Network
Mechanism of protection of retinal cells by p107 and p27
[Renewal] Granted: $300,000 over 3 years, July 2008 – June 2011
This project is a renewal of Dr. Bremner’s project, Role of Rb Effector Genes in Retinal Development. He and his team have found previously that proteins in the Rb and p27 family are necessary for the survival of rod and cone photoreceptors. Understanding how they promote survival has potential benefits for the treatment of retinal diseases where these cell types die, such as in retinitis pigmentosa. The proposed studies will determine whether it is the Rb-like or p27-like activity of p107 that is most critical for photoreceptor survival, and thus provide a clearer picture of what is required to protect photoreceptors from death. This kind of knowledge may suggest new therapies to protect these vital cells from dying, in humans with a blinding disease.
David D. EisenstatUniversity of Manitoba
Role of DLX homeobox genes in retinal development
Granted: $180,000 over 3 years, July 2008 – July 2011
Dr. Eisenstat and his team will study DLX homeobox genes (a type of transcription factor), which are genes involved in regulating the development of the mouse retina.
Dr. Eisenstat will explore whether these DLX transcription factors block the development of photoreceptors in retinal progenitors while at the same time promoting ganglion cell fate and survival. He will also examine mice missing only one DLX gene rather than two, to determine whether DLX1 or DLX2 is more important for normal retinal development. He will also identify all of the genes directly controlled by DLX transcription factors during retina development. It is important to understand the mechanisms of retinal development in a mouse model to uncover the causes of retinal disease.
Drs. Robert Koenekoop (PI), Anneke den Hollander (co-PI) and Frans Cremers (co-PI) - Ken Kirk and FriendsMcGill University
Identification and characterization of novel genes for childhood blindness
Granted: $50,000 over 1 year, July 2008 – June 2009
Leber congenital amaurosis (LCA), a retinal dystrophy, is the leading cause of congenital blindness with over 200,000 cases in the world. We currently know of 14 LCA genes that account for over 60% of the affected patients while the remaining 40% remains to be discovered.
LCA genes are discovered through detailed genetic studies involving large groups of well characterized LCA patients and their families. Gene discovery is the path way to protein discovery and gives a new understanding of how a normal retina functions, providing insights into disease mechanisms. It also improves the clinical diagnosis of this complex group of diseases providing a prognosis of the patient’s future visual performance, and basis for genetic counseling. Most importantly, LCA gene identification has led to successful recovery of vision in humans. Currently three human trials are ongoing and have proven visual recovery in older children (ages 20 years) after RPE65 gene replacement.
Dr. Koenekoop and his team at McGill University will identify and characterize new LCA genes, using a technique, where 35 new and significant homozygous regions were identified. These regions do not map to known LCA genes, and so will contain new LCA genes. This new approach has already led to the discovery of three new retinal dystrophy genes (CEP290, LCA3 and LCA5). Further investigation into the remaining 32 regions will be performed to identify new genes that cause LCA. Eventually these new LCA genes will expand or understanding of the disease but also provides new genes for visual recovery trials.
Genetic and functional analysis of novel cone photoreceptor genes
Granted: $100,000 over 2 years, July 2008 – June 2010
Dr. Mears at the Ottawa Hospital Research Institute is conducting a study in mice, whose photoreceptors have been drastically altered. This will provide the means to identify those genes that are critical for photoreceptor development. Photoreceptors are the rods and cones that capture light thereby initiating the process of vision.
The rods, which greatly outnumber the cones, do not give high visual acuity (sharp or clear vision). Rods are highly sensitive and enable us to see in the dark. The cones, which in humans are primarily concentrated in the central area of the retina, referred to as the macula and fovea, only function under bright light conditions and are responsible for sharp central vision and the perception of colour. There are many diseases which impact the retina and in most cases it is ultimately the loss of these photoreceptors that results in the impairment of vision or blindness.
By manipulating key genes that control photoreceptor development, the goal is to turn retinal stem or progenitor cells into new healthy photoreceptors that may be transplanted into diseased retinas of mice. If successful, such transplantation therapies could preserve or even restore vision in patients with retinitis pigmentosa, Leber’s congenital amaurosis, cone dystrophies and age-related macular degeneration.
David PickettsOttawa Hospital Research Institute
Epigenetic regulation of interneuron homeostasis in the mammalian retina
Granted: $270,000 over 3 years, July 2008 – June 2011
Dr. David Picketts and Dr. Valerie Wallace at the Ottawa Hospital Research Institute are studying how the Atrx gene promotes the health and survival of interneurons in the mouse retina.
Amacrine and horizontal cells are interneurons in the retina whose function is to process information from photoreceptors before it is sent to the brain and transmitted as an image. These interneurons must remain intact and receptive to continued photoreceptor signals during treatment to restore vision, however, very little is known about how the health of these cells is maintained.
Many studies examine how transplanted cells during cell transplantation or gene therapy will survive and replenish the photoreceptors, but less is known about how they establish new connections with the remaining retinal neurons.
Mice that lack the Atrx gene in the retina lose a significant proportion of their amacrine and horizontal cells after birth. By identifying the Atrx-dependent pathways and genes that promote survival of these cells, we will gain insight into how the retinal circuitry is maintained. Understanding the biology underlining the maintenance of these cells could improve the outcome of gene and cell therapy to the eye.
Molecular determinants responsible for the involvement of lecithin retinol acyltransferase, a protein of the visual cycle, in retinitis pigmentosa
Granted: $100,000 over 2 years, July 2008 – June 2010
The sensation of vision is initiated by the absorption of light by visual pigments in rod and cone photoreceptors. After this has occurred, the part of the visual pigment that is derived from Vitamin A must be regenerated, so that it can perform the same function again. This is done through a series of enzymatic reactions called the visual cycle. Mutations of several of the enzymes of the visual cycle lead to retinal degeneration. One of these enzymes is a cell membrane protein called lecithin retinol acyltransferase (LRAT).
A particular mutation of LRAT leads to the loss of its enzyme activity and causes retinitis pigmentosa. However, this mutation does not impair the enzymatic activity of LRAT. Very likely, this mutation causes loss of function either by altering binding of the mutant enzyme to the cell membrane, or by drastically changing the three-dimensional structure of the enzyme. Dr. Salesse and his team at the CHUQ research center of Laval University will test these hypotheses, by comparing the membrane-binding activity and the structure of the native (normal) LRAT enzyme with those of the mutant enzyme.
This study will enhance our knowledge of a relatively unknown family of enzymes that are crucial for retinal function. Understanding how mutation of LRAT leads to malfunctioning of the retina, is essential for developing therapies to prevent this form of RP.
Vincent TropepeUniversity of Toronto
Genetic & molecular studies of neurogenesis and regeneration in the zebrafish
Granted: $150,000 over 3 years, July 2008 – July 2011
Dr. Vince Tropepe of the University of Toronto will use the natural ability of zebrafish to regenerate retinal cells under normal and pathological conditions in order to investigate the genetic basis for tissue self-repair in the retina.
The zebrafish can regenerate all of the specialized cells in the retina, including photoreceptors (rods and cones), unlike adult human retina, which cannot naturally produce new specialized cells to replace those that are lost or damaged by diseases, such as RP, AMD, glaucoma. On almost all other levels of organization and function, the fish retina and the human retina are similar. Recent discovery of stem cells in the adult human retina suggests that there might be a hidden capacity for regeneration if researchers can find a way to properly stimulate and control them.
The goal of the research is to gain clear understanding of the molecular mechanisms controlling retinal cell regeneration. This research will provide an important foundation for investigating whether similar mechanisms can be stimulated in the human retina, which may lead to new cell-based therapies to treat retinal degenerative diseases.
Role of MMP2 in retinal regeneration
Granted: $74,375 over 2 years, July 2008 – August 2010
Dr. Tucker will utilize tissue-engineering techniques, specifically polymers that degrade following transplantation, to deliver active MMP2 (an enzyme known to degrade proteins that block regeneration) directly to injured retina in an attempt to restore vision following retinal transplantation.
Injury caused by retinal degeneration creates an inhibitory scar, at the outer areas of the retina. This scar contains molecules such as the chondroitin sulfate proteoglycans (CSPGs) that are known to stop cellular growth and movement, thus acting as a barrier to regeneration. If successful, the removal of this inhibitory barrier, by delivering MMP2, will stimulate cellular integration and vision restoration following retinal transplantation.
Graduate Student Scholarships
Robert Cantrup - Arthur J.E. Child FoundationUniversity of Calgary
The role of Zac1 in rod photoreceptor development
Granted: $60,000 over 3 years, July 2008 – June 2011
Rob Cantrup of the University of Calgary is focused on understanding how Zac1, a gene found in the retina, interacts with other genes and effector molecules to negatively regulate the formation of rod photoreceptors.
Evidence exists that in the absence of Zac1, extra rod photoreceptors are generated, while on the other hand, the overexpression of Zac1 decreases the number of rods generated.
Through genetic, molecular and cellular studies, Rob Cantrup will explain how Zac1 acts as a negative regulator of a rod fate. More specifically, Rob Cantrup will identify the genetic partners of Zac1 and the downstream genes that Zac1 regulates. He will also test if the inhibition of Zac1, which should increase photoreceptor production, would be therapeutically useful in a mouse model of RP.
In the long-term, this research may allow the manipulation of Zac1 (either alone or in combination with other genes) to be used as a preventative therapy used prior to the onset of photoreceptor loss in RP patients. While cell based therapies offer some promise for the replacement of lost photoreceptors in RP or AMD patients, the ability to generate even more photoreceptors via genetic manipulation is likely to further enhance the design of novel treatment regimes.
Linda WuThe Hospital for Sick Children
Gene regulation in retinal photoreceptor cells
Granted: $10,000, July 2008 – December 2008
Linda Wu, a Master’s student at the University of Toronto, will explore the ability of a viral vector to deliver specific genes into photoreceptor cells. Photoreceptor cells, consisting of both rod and cone cells, are a layer of retinal cells responsible for converting light energy into an image that the brain can interpret.
She will also look at ways to enhance gene expression in these cells by mixing the viral vector in different formulations. The study will determine the benefits of using this viral vector for gene delivery exclusively to photoreceptor cells.
With recent advancements in the field of gene therapy, correct genes can be delivered to the affected cells using a viral vector to help improve vision in patients. Mutations in many genes affecting photoreceptor cells lead to retinal degeneration.