Researchers uncover genetic link to age-related cataracts

CLEVELAND — July 30, 2009 — Bing-Cheng Wang, Ph.D., Case Western Reserve University School of Medicine professor of pharmacology and senior staff scientist at MetroHealth Medical Center, and Sudha K. Iyengar, Ph.D. professor of genetic and molecular epidemiology at Case Western Reserve University School of Medicine, have discovered the first gene associated with the formation of age-related cataracts, a leading causes of blindness.

Their research is part of a large-scale collaborative investigation involving 10 different laboratories from the United States, United Kingdom and Australia. The study, entitled “EphA2is associated with age-related cortical cataract in mice and humans,” will be published in the July 31 issue of PLoS Genetics.

Millions of Americans suffer from Age-Related Cataract or ARC and an estimated 4 billion dollars are spent to treat the disease in the U.S. each year. ARC is known to be highly heritable, yet even after decades of research, little is known about the genetic causes for ARC.

The lens of the eye is normally clear, allowing the transmission of focused light onto the retina. Cataracts occur when proteins in the lens become damaged and clump together — causing the lens to become cloudy and obscure vision. Researchers say EphA2 encodes an enzyme which plays a role in the repair of those damaged proteins.

Expression of the EphA2 protein occurs naturally in human and mice. It decreases with age, providing a possible explanation for age-related cataract formation. The protein, an enzyme called a tyrosine kinase, is responsible for the transfer of phosphate groups to other proteins in the lens, a process known as phosphorylation that is a common step in cell signaling. When EPHA2 is absent, unphosphorylated proteins accumulate that indicate high levels of cellular stress. Researchers believe that these underphosphorylated proteins become sticky, bunch up, and cause damaged proteins to form clusters that damage the structure and impair the clarity of the lens.

The discovery was serendipitous,” explained Dr. Wang. Initially Dr. Wang’s group was interested in testing the hypothesis that EphA2 was involved in preventing tumor formation. So his lab obtained a line of mice in which EphA2 gene had been deleted. Supporting their hypothesis, the mice without EphA2 gene became much more susceptible to tumor development, which was reported in the journal Cancer

Research two years ago. Interestingly, in addition to increased tendency to develop tumors, the mice formed cataracts as they became older. This was an exciting but totally unexpected observation. Co-incidentally, around the same time, Dr. Iyengar’s group reported in Proceedings of National Academy of Science that the same gene region was linked to human age-related cataract. By another amazing coincidence, Dr. Wang and Dr. Iyengar had offices next door to each other in the late 1990’s when they first came to Cleveland as independent scientists. They have been friends and colleagues ever since.

“After many excited phone calls and emails, a collaboration was initiated, and the rest was history,” said Wang.

So far, the groups have managed to identify several specific mutations in human EphA2 that are associated with ARC. In the future, the groups plan to search for additional mutations. They believe that this effort will allow them to better understand the specific cellular processes by which EphA2 helps maintain lens clarity.

The hope is that the identification of the underlying causes for ARC will point researchers in the direction of new treatments and preventions for ARC. Dr. Wang’s lab at Cleveland’s MetroHealth Medical Center is developing such agents.

“Our mutant mice will provide a unique platform to find out which specific molecules or cellular processes are affected by EphA2 deletion. Meanwhile, studies of human mutant EphA2 could also verify if the same molecules or cellular processes are affected in human lens,” said Wang.

By age 80, more than half of Americans will have a cataract or have had cataract surgery. Researchers say that as the population ages, ARC is becoming an increasingly large problem. Delaying the development of ARC could have a huge medical impact, both by alleviating the suffering of affected individuals and their families and by saving health care costs.

About Case Western Reserve University School of Medicine

Founded in 1843, Case Western Reserve University School of Medicine is the largest medical research institution in Ohio and is among the nation’s top medical schools for research funding from the National Institutes of Health. The School of Medicine is recognized throughout the international medical community for outstanding achievements in teaching. The School’s innovative and pioneering Western Reserve2 curriculum interweaves four themes–research and scholarship, clinical mastery, leadership, and civic professionalism–to prepare students for the practice of evidence-based medicine in the rapidly changing health care environment of the 21st century. Eleven Nobel Laureates have been affiliated with the school.

Annually, the School of Medicine trains more than 770 M.D. and M.D./Ph.D. students and ranks in the top 25 among U.S. research-oriented medical schools as designated by U.S. News and World Report “Guide to Graduate Education.”

The School of Medicine’s primary clinical affiliate is University Hospitals Case Medical Center and is additionally affiliated with MetroHealth Medical Center, the Louis Stokes Cleveland Department of Veterans Affairs Medical Center, and the Cleveland Clinic, with which it established the Cleveland Clinic Lerner College of Medicine of Case Western Reserve University in 2002. http://casemed.case.edu.

About The MetroHealth System

The MetroHealth System is one of the nation’s largest public health providers, ranking in the top 1% of all hospitals nationwide for quality in patient care. As the region’s only Level I adult and pediatric trauma and burn center, MetroHealth is a nationally-recognized leader in critical care and rehabilitation, community health, high-risk perinatal care, and senior health.

MetroHealth offers the region’s largest urban-based network of community health centers focused on reducing health disparities through comprehensive care to vulnerable populations. MetroHealth achieved Magnet designation in 2005, the nation’s highest honor for nursing excellence, and was chosen as one of the 2007 Top 100 Hospitals nationwide by Thomson Healthcare.

Founded in 1837, MetroHealth has been a major affiliate of Case Western Reserve University since 1914 and all MetroHealth physicians are CWRU faculty. MetroHealth is Cleveland’s tenth largest employer with more than 6,500 employees. For more information on The MetroHealth System, visit www.metrohealth.org.

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