Regenerating the Retina to Restore Sight in the Blind

Age-Related macular degeneration (AMD) is the most common cause of blindness in the UK affecting one in three individuals by the age of 75. The condition results in a loss of central vision due to extensive damage to the retina, making it difficult to read and recognise appearances. Currently, there is no significant treatment for the condition as human retinal cells cannot regenerate once damaged, and the only way to restore sight is via the use of a donor retina. However, new research has shown the potential to reverse blindness with the discovery of specific stem cells present in the eye, with the ability to specialise into mature photoreceptor (light-detecting) cells.

The macula is a highly-pigmented oval-shaped spot located in the centre back of the retina and is responsible for accurate focussing. A typical symptom of dry (non-neovascular) AMD is the accumulation of yellow spots called drussen in and around the macula, leading to the loss of central vision. Wet (neovascular) AMD occurs when new blood vessels begin to grow abnormally beneath the retina and cause a severe loss of vision, as the vessels begin to leak blood and fluid into the retina damaging the light-detecting retinal cells. In both forms of AMD, the loss of vision is currently irreversible.  Source: Marilyn Haddrill, (2014), Understanding Age-related Macular Degeneration (AMD) http://www.allaboutvision.com/conditions/amd.htm

The macula is a highly-pigmented oval-shaped spot located in the centre back of the retina and is responsible for accurate focussing. A typical symptom of dry (non-neovascular) AMD is the accumulation of yellow spots called drusen in and around the macula, leading to the loss of central vision. Wet (neovascular) AMD occurs when new blood vessels begin to grow abnormally beneath the retina and cause a severe loss of vision, as the vessels begin to leak blood and fluid into the retina damaging the light-detecting retinal cells. In both forms of AMD, the loss of vision is currently irreversible.
Source: Marilyn Haddrill, (2014), Understanding Age-related Macular Degeneration (AMD)
http://www.allaboutvision.com/conditions/amd.htm

The limbal neurosphere (LNS) stem cells are located at the forefront of the eye between the transparent cornea and the white opaque sclera. Unlike standard stem cells, the LNS cells have previously started to develop into specialised eye cells and may still have the potential to differentiate into different types of retinal cells. The study, carried out by leading researchers at the University of Southampton and University of Bristol, investigated if LNS cells extracted from human and mouse eye tissue would differentiate into retinal cells in a laboratory environment. LNS cells were extracted from the limbal tissue of donated human eyes from adults up to 97 years of age. The cells were cultured under different conditions within a laboratory environment and grown with retinal cells from new born mice and encouraged to develop into mature retinal cells. The process was repeated using LNS cells from adult mice alone and transplanting them into the retina of new-born mice. Gene expression of the LNS cells was monitored carefully and compared to the typical genes expressed in mature light-detecting retinal cells.

Results showed that some LNS cells from the adult mice portrayed markers, indicating that they had differentiated into mature photoreceptor retinal cells when transplanted into new-born mice. However, the cells did not assimilate into the retina. Human LNS cells cultured with retinal tissue from mice in a laboratory environment showed vague signs of developing into retinal tissue, but did not produce mature photoreceptor markers. Researchers concluded that the human LNS cells were unable to distinguish into a retinal lineage under the given conditions, as there may be a more intricate mechanism involved with human limbal tissue than mice LNS cells.

Advanced research and trials are now required to identify the exact conditions under which human LNS cells may be able to differentiate into light-detecting retinal cells and integrate into the retina. However, “as a readily accessible progenitor cell resource that can be derived from individuals up to 97 years of age, limbal neurosphere cells remain an attractive cell resource for the development of novel therapeutic approaches for degenerative retinal diseases,” including macular degeneration.

 

Original Article: Xiaoli Chen, Heather Thomson, Jessica Cooke et al, (2014), Adult Limbal Neurosphere Cells: A Potential Autologous Cell Resource for Retinal Cell Generation. PLOS One

http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108418#close

Further reading: http://www.nhs.uk/news/2014/10October/Pages/Scientists-look-into-regenerating-retinal-cells.aspx

Feature Image: http://www.health.com/health/package/0,,20681758,00.html

 

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