A Field of Dreams for Vision Research

By Jason Socrates Bardi

"But from thine eyes my knowledge I derive,
And, constant stars, in them I read such art."

——William Shakespeare, from Sonnet XIV, circa 1594

"If you build it, they will come," was the oft-repeated line from the 1989 film Field of Dreams, which told the story of a farmer who had a vision to build a baseball diamond in the middle of his cornfield.

No single line more accurately describes the work of a handful of researchers at The Scripps Research Institute (TSRI) who for the last several years have been building their own diamond dream—collaborations and multidisciplinary research projects that aim to make an impact in the field of vision research and to touch lives by finding an approach to treating ocular diseases.

And now this work is beginning to attract attention. The National Eye Institute (NEI) and the rest of the vision research world is beginning to recognize TSRI, with its team of interdisciplinary researchers, as a major center for vision and eye research—research that is critically important, since vision loss does and will continue to affect the quality-of-life in our aging society.

"Virtually every American has one of the diseases or knows somebody who has one of the diseases that could be effectively treated if we develop a drug to prevent abnormal growth and function in the eye," says Martin Friedlander, associate professor in the Department of Cell Biology and chief of the Retina Service in the Division of Ophthalmology, Department of Surgery at Scripps Clinic.

Building Upon Past Successes

The latest recognition of the vision research at TSRI is a $9.6 million NEI grant, which was recently awarded to Friedlander and several other investigators at TSRI to take basic science observation as close to the clinic as possible.

The grant, titled Fragments of TrpRS to Treat Neovascular Eye Disease, also includes TSRI investigators Paul Schimmel, who is Ernest and Jean Hahn Professor of Molecular Biology and Chemistry and a member of the Skaggs Institute for Chemical Biology; Dale L. Boger, Richard and Alice Cramer Professor of Chemistry; Professor David Cheresh and Associate Professor Glen Nemerow, both of TSRI's Department of Immunology; and Gary Siuzdak, Adjunct Associate Professor of the Department of Molecular Biology.

For Friedlander, the grant is testament to the fact that TSRI is the perfect place for such a project, since it combines first-rate basic vision science with the nearby clinical resources of the Scripps Clinic. The program, which is already up and running, was favorably reviewed and funded by the NEI, and in part, this was because of the existing collaborations of the grant's investigators and the high potential this work has to translate bench work to the bedside.

For instance, Friedlander and Nemerow already participate in the NEI-funded Core Center for Vision Research at TSRI, which began operations last summer, providing shared support resources for 11 TSRI researchers and six researchers from the University of California, San Diego (UCSD) who have independent programs in vision science funded through the NEI.

The Core Grant for Vision Research supports several core facilities to provide additional resources for the independent programs of these researchers and others doing vision science research. A microarray core module produces DNA "chip" microarrays that can be used for observing changes in gene expression during the course of normal and pathological changes in the eye. Similarly, a proteomics core module provides global analysis of all the proteins expressed. A microscopy and imaging core module allows the phenotypic state of eye tissue to be studied in conjunction with the expression data that comes from the microarray and proteomics cores, taking advantage of a new state-of-the-art multiphoton scanning laser confocal microscope.

In May, a $500,000 supplement for technology enhancement was awarded to Friedlander for one of his grants from the National Eye Institute. These funds were used to purchase a new Maldi-TOF spectrometer and additional imaging equipment to further expand resources available to TSRI and UCSD vision researchers already working together through the Core Grant for Vision Research.

"We are very excited about this [new] interdisciplinary project to study a very exciting new anti-angiogenic and delivery systems that will enable us to bring it to sites of abnormal ocular angiogenesis," says Friedlander. "We are particularly grateful to the NEI for providing the resources to establish this program."

Angiogenesis and Vision Loss

The vast majority of diseases that cause catastrophic vision loss do so as a result of abnormal vessel growth in the back of the eye. In fact, the leading cause of vision loss in patients who are above the age of 65 is macular degeneration.

"Twelve to fifteen million people in this country alone have macular degeneration," says Friedlander. "And 10 to 15 percent of them will suffer acute loss of central, or 'reading,' vision."

In patients under the age of 65, the leading cause of vision loss is due to a complication of diabetes known as diabetic retinopathy. Some 16 to 18 percent of the U.S. population has diabetes. Virtually every one of those patients will eventually have a form of diabetic retinopathy after 20 years, says Friedlander, and every year 40,000 of them lose vision.

Both macular degeneration and diabetic retinopathy are characterized by angiogenesis, or the development of abnormal blood vessel growth in the eye. In the case of macular degeneration, new blood vessels grow under the retina. In diabetic retinopathy, abnormal vessels grow on top of the retina. The effect is much the same; the vessels interfere with normal structures or the transmission of light to the back of the eye, impeding vision.

There is currently no effective treatment for the vast majority of these patients. For several years, researchers have sought compounds that inhibit angiogenesis and curtail the diseases.

There are several anti-angiogenic compounds in clinical trials. But one of the more promising, says Friedlander, is TrpRS, the one the TSRI researchers will be developing with the NEI funding.

"People typically talk about 20, 30, 40 percent inhibition [of new vessel formation] for the compounds that are in clinical trials," says Friedlander. "What we have seen in our pre-clinical studies is that in 70 percent of cases, you get 100 percent inhibition."

"Our hope is that TrpRS may be something we someday use to treat patients with neovascular eye disease."

TrpRS and the Autoregulation of Angiogenesis

The original work started with Schimmel, who had been studying RNA synthetases for a number of years.

After a gene is transcribed from double-stranded DNA into a single-stranded form of RNA called messenger RNA (mRNA), a large molecule called the ribosome translates the mRNA into a protein. The ribosome recognizes another type of molecule, transfer RNA (tRNA), which brings the ribosome the amino acids from which it constructs proteins.

One of the first steps of protein synthesis involves "charging" the tRNA molecules with the amino acids, and this step is carried out by a set of molecules known as tRNA synthetases. TrpRS, for instance, charges tRNA molecules with the amino acid tryptophan. Since protein synthesis provides the raw material during angiogenesis, tRNA synthetases play a big role. And, indeed, several years ago, Schimmel showed that a full length tyrosine tRNA synthetase served as a pro-angiogenic molecule.

Noticing that another similar enzyme, the tryptophanyl tRNA synthetase "TrpRS", had similar motifs as the tyrosine enzyme, Schimmel and his laboratory reasoned that like the tyrosine tRNA synthetase, the TrpRS would promote angiogenesis. Much to his amazement, however, TrpRS not only was not a promoter of angiogenesis—it actually inhibited the process.

This was a surprising result, since one would not expect a molecule involved in protein synthesis and cell proliferation to be involved in shutting down that same proliferation.

"Then," says Schimmel, "a talented postdoctoral student in our laboratory—Kei Wakasugi—had the original idea that a fragment of human TrpRS could be active in angiogenic pathways."

Interestingly, two naturally occurring, shortened forms of the molecule proved to be even more powerful inhibitors of angiogenesis. These truncated forms are either made after one end of the full-size TrpRS is chopped off by proteolysis or they are synthesized from an "alternatively spliced" mRNA, which has been rearranged by the cell before the ribosome uses it to make a protein.

Wakasugi and others in the laboratory did many tests and established that the TrpRS fragments were, indeed, inhibitors of angiogenesis in cell culture. But Schimmel and his laboratory wanted to test the TrpRS fragments using more powerful models, such as those that Friedlander had already developed over the course of studying angiogenesis for several years. In this model system normal vessel formation in the eye resembles, in many ways, the type of angiogenesis observed in human neovascular eye disease.

"We were then fortunate to have wonderful collaborators here at The Scripps—the laboratories of Marty Friedlander and David Cheresh—who gave us the opportunity to then extend the work by testing two of the fragments in animal models that they had specifically developed for angiogenesis," says Schimmel.

In the subsequent experiments, they confirmed the earlier findings and extended them by demonstrating the TrpRS fragments were potent anti-angiogenics.

The fact that TrpRS is a naturally occurring protein may make it an even more effective treatment because it will not have the same problems of toxicity and immunogenicity that plague some other potential drugs.

"Moreover," says Friedlander, "this is something that we can teach the cell how to make." One clinical approach to treating angiogenic vision loss, he says, could be to deliver the TrpRS molecules directly into the eye through gene- and cell-based vectors.


Next Page | What the Grant Will Do

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Associate Professor Martin Friedlander is lead investigator for the $9.6 million National Eye Institute grant.


TSRI investigator Paul Schimmel (above) gives credit to "a talented postdoctoral student," Kei Wakasugi, for coming up with the idea that a fragment of human TrpRS could be active in angiogenic pathways.


Investigator Dale L. Boger says, "It is only through the coordinated efforts of several superb groups that a problem of such a magnitude could be attempted."


Professor David Cheresh has been working on a delivery system that selectively targets the cells that form new blood vessels in angiogenesis without influencing the normal blood vessels or any other tissue.


Investigator Glen Nemerow has been researching a separate approach that involves using adenovirus vectors as delivery vehicles.


"This effort represents one of the true strengths of TSRI, in that individuals from very different areas of research can combine their expertise to tackle scientifically fundamental, yet medically important, problems," says investigator Gary Siuzdak.