Spliceosome-Mediated RNA Trans-Splicing Therapy and Protein Replacement in Rett Syndrome
Stuart Cobb, PhD | University of Edinburgh
Targeting MeCP2 can be done either at the DNA, mRNA or protein level. Stuart Cobb is working on all of these approaches in parallel. His work with gene therapy is being done as part of the Gene Therapy Consortium.
We know that both the DNA and protein approaches might have a complication due to potential dosage issues (too much MeCP2 may be harmful). So Dr. Cobb is also pursuing an alternative technology called Spliceosome-Mediated RNA Trans-Splicing (SMaRT). This technology allows a mutation to be spliced out and repaired in RNA, the intermediate between DNA and protein in the cell. The advantage is that this approach avoids any potential over-expression issues that could result from directly modifying DNA or giving extra protein. Dr. Cobb’s approach aims to correct mutations in the intermediate RNA transcript, allowing the MECP2 gene and the MeCP2 protein product to remain under normal gene expression controls.
SMaRT technology will take advantage of the fact the RNA transcripts are edited (spliced) to make smaller molecules that contain the final blueprint for making the protein. Regions of the RNA transcript that are spliced out, linked together, and part of the final edited RNA are called exons, and the regions that are spliced out of the RNA transcript and not used are called introns. Dr. Cobb’s approach will use an engineered MeCP2 RNA that contains a sequence of spliced-out intron 2 followed by a correct exon 3 and exon 4. The intron 2 sequence allows the engineered RNA to bind to the mutated MeCP2 RNA at the matched intron 2 sequence location. Then, during RNA splicing, the alternative and correct exon 3 and exon 4 can be used to create the final RNA molecule and protein blueprint, free of mutations. Since almost all RTT mutations occur in exon 3 or exon 4, Dr. Cobb predicts that 97% of RTT-causing mutations could be corrected with this approach.
Once the SMaRT approach is optimized, it will be tested in mice with the full human MECP2 locus that contains the MeCP2 gene and all of its regulatory elements, to determine if this approach can be used in humans. If SMaRT technology works in mice and with mice engineered to contain human MeCP2 mutations, it could become a therapy for clinical development in Rett Syndrome patients.