Sci. Aging Knowl. Environ., 11 June 2003
Coming Into Focus
New lens-regeneration secrets might improve cataract treatment
R. John Davenporthttp://sageke.sciencemag.org/cgi/content/full/sageke;2003/23/nw85
Key Words: lens fiber epithelium mesenchyme
BARGA, ITALY--The years might still pass in a blur, but vision in old age could remain crystal clear if new work pans out. The results suggest that rodents possess unexpected lens-regenerating capabilities, and they also reveal signaling mechanisms that underlie lens replenishment. The findings might lead researchers to improved methods for treating cataracts.
Each year, millions of elderly Americans develop cataracts. During this process, the eyes' lenses thicken and lose their transparency. Surgically removing the lenses and replacing them with artificial ones restores vision, but the injury inflicted by the procedure frequently triggers a second bout of cataracts.
To improve therapeutic strategies, researchers are studying the capacity of lenses to regenerate. Some animals--such as newts--grow new, complete lenses if theirs are removed. Cells from the upper part of the newt iris--the colored part of the eye--can morph into lens cells and multiply to form a normal lens. Cells from the lower part of the iris, however, do not possess this power. Eye researcher Panagiotis Tsonis of the University of Dayton, Ohio, and colleagues wondered what was different about the two types of cells.
The researchers had previously identified numerous genes that were active in the upper cells but not in the lower ones, and they knew that several of these genes promote development of the eye during embryonic growth. The group added each gene to a different sample of cells from the lower portion of the eye, implanted them into newt eyes, and found that none of the animals grew new lenses. But when the team first treated cells with retinoic acid--the active form of vitamin A, which helps establish body patterns during embryonic development--iris cells carrying one of the genes formed a lens. That gene encodes a gene-activating protein known to contribute to embryonic eye formation. The group is planning further experiments to uncover its targets in iris cells, says Tsonis.
The researchers then turned their attention to mammals. Previous experiments had perturbed the protein pouch that envelops the lens, so the researchers removed lenses from mice without causing as much disturbance. After several weeks, the animals regrew lenses, apparently derived from residual lens cells in the pouch, says Tsonis. The lenses are full-size and have proper structure, he adds, and the animals respond to visual stimuli. Tsonis proposes that humans might regrow lenses if surgeons gently removed cataracts but not the surrounding tissue and didn't insert an artificial lens.
The study shows that mice harbor more regenerative capacity than previously thought, says physiologist Gordon Duncan of the University of East Anglia in Norwich, U.K. Whether a similar ability in humans would suffice to restore lenses is unclear, he says, because regrowth might take impracticably long. Duncan adds that understanding the signals that rejuvenate lenses in the newt and other animals could help focus eye cells on that path and distract them from forming scar tissue.
--R. John Davenport
June 11, 2003 Citation: R. J. Davenport, Coming Into Focus. Sci. SAGE KE 2003, nw85 (11 June 2003)
Science of Aging Knowledge Environment. ISSN 1539-6150