'New technique reverses blindness in mice'

Scientists have reversed congenital blindness in mice for the first time using a technique that may lead to new treatments for humans.

The researchers from Icahn School of Medicine at Mount Sinai in the US reversed congenital (present from birth) blindness in mice by changing the supportive cells in the retina called Muller glia into rod photoreceptors.

The findings advance efforts towards regenerative therapies for blinding diseases such as age-related macular degeneration and retinitis pigmentosa, researchers said.

"This is the first report of scientists reprogramming Muller glia to become functional rod photoreceptors in the mammalian retina," said Thomas N Greenwell from the US National Eye Institute (NEI).

"Rods allow us to see in low light, but they may also help preserve cone photoreceptors, which are important for colour vision and high visual acuity," Greenwell said.

"Cones tend to die in later-stage eye diseases. If rods can be regenerated from inside the eye, this might be a strategy for treating diseases of the eye that affect photoreceptors," he said.

Photoreceptors are light-sensitive cells in the retina in the back of the eye that signal the brain when activated.

In mammals, including mice and humans, photoreceptors fail to regenerate on their own. Like most neurons, once mature they don't divide.

In the first phase of a two-stage reprogramming process the team spurred Muller glia in normal mice to divide by injecting their eyes with a gene to turn on a protein called beta-catenin.

Weeks later, they injected the mice's eyes with factors that encouraged the newly divided cells to develop into rod photoreceptors.

The researchers used microscopy to visually track the newly formed cells. They found that the newly formed rod photoreceptors looked structurally no different from real photoreceptors.

In addition, synaptic structures that allow the rods to communicate with other types of neurons within the retina had also formed.

To determine whether the Muller glia-derived rod photoreceptors were functional, they tested the treatment in mice with congenital blindness, which meant that they were born without functional rod photoreceptors.

In the treated mice that were born blind, Muller glia-derived rods developed just as effectively as they had in normal mice.

Functionally, they confirmed that the newly formed rods were communicating with other types of retinal neurons across synapses.

Light responses recorded from retinal ganglion cells - neurons that carry signals from photoreceptors to the brain - and measurements of brain activity confirmed that the newly-formed rods were in fact integrating in the visual pathway circuitry, from the retina to the primary visual cortex in the brain.