01 February 2017

Gene therapy of dystrophic epidermolysis bullosa

Severe hereditary skin disease cured by genome editing

Anna Manshina, N+1

Chinese biotechnologists have tested CRISPR/Cas9 genome editing technology on a mouse model for the treatment of severe hereditary skin disease. Scientists used a new delivery method and improved the accuracy of the "genomic scissors" by using the Cas9 ribonucleoprotein complex and the RNKsgRNA guide. An article about the study was published in the journal Proceedings of the National Academy of Sciences (Wu et al., Efficient in vivo gene editing using ribonucleoproteins in skin stem cells of recessive dystrophic epidermolysis bullosa mouse model).

Dystrophic epidermolysis bullosa (DBE) – severe genetic skin disease in humans. It is caused by a mutation in the Col7a1 gene, due to which non-working type VII collagen is formed. Such collagen poorly binds the inner layers of the skin with the outer ones, as a result of which the epidermis lags behind in patients with DBE at the slightest mechanical impact. 

Today there is only symptomatic treatment of DBE, it is not completely curable. The development of radical treatment is carried out in three directions: protein, cell and gene therapy. Treatment at the gene level is the most promising direction, it can remove the cause of the disease, the Col7a1 mutation.

In the new work, scientists used the CRISPR/Cas9 genome editing system to treat DBE. This system is based on the action of the bacterial protein Cas9, which finds a mutant section of DNA and cuts it out. After that, the cell triggers the natural DNA repair mechanism.

As a model of human disease, scientists used a mouse line containing a point mutation in the 80 exon of the Col7a1 gene. Biologists have suggested that for the therapy of DBE, it is enough to remove this mutant exon from the gene, after which a shortened but functional version of collagen should be formed.

At the first stage of the experiment, to deliver the genome editing system to tissues, scientists used plasmids (ring DNA molecules), which encode both the guide RNA, which finds a target for editing, and the protein-nuclease Cas9. After penetration into the cells, these plasmids began to work and Cas9 synthesis took place already in place. However, the results of this preliminary experiment were not very good due to the fact that plasmids did not penetrate well into the right tissues. Therefore, instead of plasmids, it was decided to inject mice with a ready–made complex for genome editing - ribonucleoprotein Cas9/sgRNA. This complex consists of a Cas9 protein and an RNA guide that directs the protein to the damaged DNA.

This method of delivery worked, the complex got into the right tissues and in sufficient quantity to fix the damaged gene. After treatment, the connection between the inner and outer layers of the skin in mice doubled, from thirty to sixty percent. The scientists also noted that the use of Cas9/sgRNA ribonucleoprotein may be safer than plasmids. The complex does not replicate in a living cell, which means that it reduces the likelihood that other genes that are similar to mutant ones will be damaged during therapy. However, clinical trials are still far away, additional data on the long-term effects of treatment are needed.

CRISPR/Cas9 is a simple and variable gene therapy technology. It can be used to treat hereditary blindness and various genetic diseases, and the startup Editas Medicine promises to edit the genome this year.

Portal "Eternal youth" http://vechnayamolodost.ru  01.02.2017

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