Monday, 16 April 2012

Algal Genes giving Sight to the Blind


The Idea
A gene in algae is known to produce a protein, Channelrhodopsin-2 (ChR2), which is light sensitive.  Common blindness is caused by the loss of photoreceptive cells in the retina of the eyes, so it was hypothesised that if this gene were injected in a virus into the eyes of a blind mouse, cells previously used as messengers to relay information out of the retina could work as photoreceptors themselves (Doroudchi et al, 2011).  Once the gene began working in these cells the ChR2 would be produced and the light sensitive protein would give sight back to the mouse.  If this worked and had no ill-effects, it would be likely that this process could work on blind humans as well (Puiu, 2011).
The Method
A selection of blind mice were given subretinal injections of either a saline solution (as a control test) or of what was dubbed a ‘tame virus’ containing the necessary algal gene.  After ten weeks the mice were dissected and ChR2 protein was found in the retinal cells of the treated mice. This meant that the gene was functioning properly and the light sensitive protein should be passing information to cells able to send messages to the brain. Practical tests were done on other treated mice to see if they would respond to light stimulus.  Each mouse was positioned in the centre of a maze with six corridors and a light was shone from the corridor which led to the exit.  The mice with sight quickly learnt to immediately go to the lit corridor, while the untreated blind mice had to rely on luck to find the exit (Doroudchi et al, 2011).
The Findings
The treated mice were able to escape the maze with a mean time of 7 seconds by the end of the training period, untreated mice took on average 19 seconds and normal sighted mice escaped with a mean time of 2.6 seconds.  To test the longevity of this treatment, after 10 months the mice were tested again and still performed significantly better than the untreated blind mice (Doroudchi et al, 2011).
The Future
That the mice were able to escape the maze an average of 2.5 times faster than untreated mice, led to the conclusion that they had at least some perception of the presence of the light.  After 10 months the mice were still able to see as well as they could 10 weeks after the injection and researchers concluded that the gene in the retinal cells was still working to produce the required ChR2 (Doroudchi et al, 2011). 
The findings from safety tests to ensure the virus had not spread showed that the gene was confined to the cells it had been intended for and that the mice were experiencing no ill-effects.  The conclusion of the investigation states that “data indicate that virally delivered ChR2 can provide a viable clinical therapy for photoreceptor disease-related blindness” (Doroudchi et al, 2011) and within two years human trials may even be attempted (Hooper, 2011).  With positive results this product may soon be commercially available and blind people may have the huge benefit that it provides.

Bibliography

Doroudchi, M. M. et al (2011). Virally delivered Channelrhodopsin-2 Safely and Effectively Restores Visual Funcion in Multiple Models of Blindness. Molecular Therapy, 1220-1229,
doi: 10.1038/mt.2011.69
 Hooper, R. (2011). Genes from algae allow blind mice to see. New Scientist, Issue: 2808  <http://www.newscientist.com/article/mg21028083.100-genes-from-algae-allow-blind-mice-to-see.html?full=true>
Puiu, T. (2011, April 14). Algae gene therapy could cure blindness. Retrieved March 16, 2012, from ZME science: http://www.zmescience.com/medicine/genetic/algae-gene-therapy-could-cure-blindness-3425435/



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