Future File is a Retinal Physician feature designed to highlight new and innovative early-stage and preclinical concepts that could one day help to advance the everyday practice of retina specialists.

New Approach to Overcoming Anti-VEGF Resistance

■ An international team of researchers led by Baylor College of Medicine and Houston Methodist has discovered a strategy that can potentially address a major challenge to the current treatment for choroidal neovascularization (CNV) — resistance to anti-VEGF therapies. Up to one-fourth of all anti-VEGF-treated patients are unresponsive to this treatment and about one-third of the responders become resistant to it after repeated administration over time.

Working with a mouse model they developed, the researchers found that combining apolipoprotein A-I binding protein (AIBP) with anti-VEGF overcomes anti-VEGF resistance and effectively suppresses CNV. The findings open the possibility of reducing anti-VEGF resistance in patients in the future. The study appears in the journal Communications Biology.

Blood Protein Could Be a Key to Combating Dry AMD

■ Scientists at Sanford Burnham Prebys Medical Discovery Institute have shown that the blood protein vitronectin is a promising drug target for dry AMD. The study, published in the Proceedings of the National Academy of Sciences (PNAS), also holds implications for Alzheimer and heart disease, which are linked to vitronectin.

“Our findings suggest that vitronectin, which is shaped like a sticky propeller, orchestrates the formation of the spherical deposits that accumulate and cause dry AMD,” says Francesca Marassi, PhD, director of the Cancer, Molecules, and Structures Program at Sanford Burnham Prebys and senior author of the study. “With this information, we can look for drugs that prevent the deposits from forming and help people retain their sight for as long as possible.”

Marassi is working with scientists at the Institute’s Conrad Prebys Center for Chemical Genomics to identify vitronectin-targeting compounds that can stop drusen from forming. This drug candidate would hold promise as a treatment that slows the progression of dry AMD and potentially other plaque-related conditions. Vitronectin is also a major component of the amyloid plaques linked to Alzheimer disease and the cholesterol-rich plaques that cause heart disease.

Protein Links AMD and Retinitis Pigmentosa

■ A team of biomedical researchers at the University of Houston is now tackling both AMD and retinitis pigmentosa by exploring a protein in the retina that links them: peripherin2 (prph2). Prph2 is essential for the structure and function of the outer segments of the retinal photoreceptors.

“Mutations in peripherin 2 are associated with a variety of retinal degenerative diseases, including retinitis pigmentosa, cone-rod dystrophy and multiple forms of macular dystrophy,” said Muna Naash, PhD, the principal investigator. “Peripherin2 mutations can also cause secondary defects in adjacent tissues, including the retinal pigment epithelium and choroid, which hampers the development of therapeutics for these diseases.” The work is funded by a $2.5 million grant from the National Eye Institute.

Absence of Enzyme Is Common to Wet and Dry AMD

■ Researchers have successfully treated AMD in mice after finding an unexpected link between the 2 main forms of the disease, the leading cause of vision loss in people 60 and older. Researcher Brad Gelfand, PhD, of the University of Virginia (UVA) School of Medicine and the UVA School of Engineering, cautions that his team is far from being able to use the approach in patients with AMD, but he is excited about the potential it holds. “It’s not as if this is the final answer to the problem, but it’s certainly a big step along the way, hopefully,” he said.

The new discovery links dry and wet macular degeneration in a surprising way. Gelfand has focused primarily on the more common, and currently untreatable, dry form. But after making a discovery about dry AMD, he went on to determine that the finding held true for wet AMD as well. “When we first saw the results, I was very surprised,” he said.

Gelfand, of UVA’s Center for Advanced Vision Science, found that the absence of a particular enzyme could drive both forms of AMD. The enzyme, called Dicer, is lost with age, and that loss leads to an overgrowth of blood vessels in the retina and other damage, he and his team determined. Developing a Dicer-based treatment will likely take several years if all goes well. For now, though, Gelfand’s discovery has shed light on the poorly understood relationship between the 2 forms of AMD. “It certainly solidifies the idea that wet and dry AMD share a lot of mechanisms,” he said.

Tooth Enamel Protein Found Present in Dry AMD

■ A protein that normally deposits mineralized calcium in tooth enamel may also be responsible for calcium deposits in the back of the eye in people with dry AMD, according to a study from researchers at the National Eye Institute (NEI). This protein, amelotin, may turn out to be a therapeutic target for the blinding disease. The findings were published in the journal Translational Research.

“Using a simple cell culture model of retinal pigment epithelial cells, we were able to show that amelotin gets turned on by a certain kind of stress and causes formation of a particular kind of calcium deposit also seen in bones and teeth. When we looked in human donor eyes with dry AMD, we saw the same thing,” said Graeme Wistow, PhD, chief of the NEI Section on Molecular Structure and Functional Genomics and senior author of the study.

Key Protein Structure of PDE6 Enzyme Is Modeled

■ Researchers at the University of New Hampshire have reported the first structural model for a key enzyme, and its activating protein, that can play a role in some genetically inherited eye diseases like retinitis pigmentosa and night blindness.

“There has been substantial research on the biochemical pathway involving this enzyme, known as PDE6, but defining atomic-level models is important for locating PDE6 mutations to understand why they cause disease and how we can develop new therapeutic interventions to manage retinal diseases,” said Rick Cote, director of the Center of Integrated Biomedical and Bioengineering Research and principal investigator on the study. In the study, published in the Journal of Biological Chemistry, researchers reported how they were able to use chemical cross-linking combined with mass spectrometric analysis to resolve the structure of PDE6 in its nonactivated and transducin-activated states. This approach permitted visualization of flexible regions of individual PDE6 catalytic and inhibitory subunits that were poorly resolved in previous work as well as the overall molecular architecture of the activated protein complex.

“Determining the structure of these visual signaling proteins has always been a challenge because of their complexity,” said Michael Irwin, doctoral student in biochemistry and lead author. “Having detailed structural information about how PDE6 is activated by transducin will help us understand the molecular causes of visual disorders and blinding diseases resulting from mutations in these proteins.”

Microglia May Have Important Role in Uveitis

■ Researchers at Massachusetts Eye and Ear have shown that microglia, the primary immune cells of the central nervous system — including the retina — serve as “gatekeepers,” or biosensors and facilitators, of neuroinflammation in a preclinical model of autoimmune uveitis. In a report published online in Proceedings of the National Academy of Sciences, the researchers describe for the first time a role for microglia in directing the initiation of autoimmune uveitis by orchestrating the inflammatory response within the retina. In reaction to disease induction, microglia closely associate with the retinal vasculature and facilitate inflammatory immune cell entry past the blood–brain barrier into the retina. When the researchers depleted microglia in this model, they observed that the disease was completely blocked.

“Our results provide clear evidence that, in the context of uveitis, microglia can facilitate entry of inflammatory immune cells into the retina and enable the host immune responses to attack cells that are not normally recognized by the immune system,” said senior author Kip M. Connor, PhD. “Until now, the role of microglia in retinal disease has not been fully understood, but our research shows for the first time that these cells serve as gatekeepers from the immune system to the central nervous system. This gateway not only has implications for treating uveitis but may provide future avenues for drug delivery across the blood–brain barrier for other diseases of the central nervous system.”

A Second Protein May Contribute to DME

■ Current therapies for this disease block the protein VEGF, which contributes to abnormal blood vessel growth. However, because the treatment is not adequate for more than half of patients with diabetic macular edema, investigators have long suspected that more factors drive vision loss in these patients. In a recent study using mice, lab-grown human retinal cells, and patient samples, Johns Hopkins Medicine scientists say they found evidence of a new pathway that may contribute to DME.

In the new study, the researchers say they found compelling evidence that angiopoietin-like 4 is at play in macular edema. The signaling protein is already well known to be a blood vessel growth factor with roles in heart disease, cancer, and metabolic diseases, of which diabetes is one. A report on the findings was published in the Journal of Clinical Investigation.

New Therapeutic Target for Diabetic Retinopathy

■ About 1 in 3 diabetic patients develops diabetic retinopathy (DR), which can impair vision and lead to blindness. A new study in the American Journal of Pathology provides clear evidence that high glucose increases the levels of enzymatic precursor, lysyl oxidase propeptide (LOX-PP), that promotes cell death, which was verified in an animal model of diabetes. These findings may help develop novel DR treatments by targeting LOX-PP or its metabolites.

“We found that hyperglycemic and diabetic conditions increased LOX-PP levels,” explained lead investigator Sayon Roy, PhD, of the Boston University School of Medicine. “LOX-PP may induce cell death by compromising a cell survival pathway, and in retinas of diabetic rats, increased LOX-PP contributed to retinal vascular cell death associated with DR. Administration of recombinant LOX-PP alone was sufficient to induce cell death. This report shows novel functionality of LOX-PP in mediating cell death under high glucose condition in retinal endothelial cells as well as in diabetic animals.”

“Our findings suggest a novel mechanism for high glucose-induced cell death involving LOX-PP, which may be a therapeutic target in preventing retinal vascular cell loss associated with DR,” noted Dr. Roy. RP