Excitatory/inhibitory neuronal reporter imaged in rat hippocampal neuronal cultures. Credit: Alexei Bygrave, Johns Hopkins Medicine
Key Points:
- A proof-of-concept study has introduced a potential new way to deliver gene therapy.
- The work exploits alternative spliced messenger RNA, which can be delivered into cells via a benign virus.
- In blind mice, the packages helped produce PRPH2 proteins in their photoreceptors.
Johns Hopkins Medicine researchers say they have successfully used a cell’s natural process for making proteins to “slide” genetic instructions into a cell and produce critical proteins missing from those cells. If further studies verify their proof-of-concept results, the scientists may have a new method for targeting specific cell types for a variety of disorders, including neurodegenerative diseases, forms of blindness and even some cancers.
According to the research team, the two methods currently used to deliver protein-making packages into cells vary widely in their effectiveness in both animal models and people.
“We wanted to develop a gene expression delivery tool that’s broadly useful in both preclinical and clinical models,” said Seth Blackshaw, professor of neuroscience and member of the Institute for Cell Engineering at the Johns Hopkins University School of Medicine.
The new study, published in Nature Communications, builds off previous research by Johns Hopkins Assistant Professor of Pathology Jonathan Ling, who published “maps” depicting how various cell types use alternative splicing of messenger RNA to construct genetic templates that produce an ever-changing set of proteins in the cell. The changes depend on a cell’s type and location. Cells normally use alternative splicing to vary the types of proteins a cell can make.
Guided by these “maps,” Blackshaw and colleagues made packages of alternative spliced messenger RNA that could be delivered into cells via a benign virus. They dubbed the packages SLED, for splicing-linked expression design.
When the package slides into a cell, it opens there. Because the SLED system is not naturally integrated into the genome, the research team then added genetic “promoters” that spark the production of proteins from the packaged SLED product.
The researchers constructed SLED systems for laboratory-cultured excitatory neurons and photoreceptors and were able to produce proteins exclusively in those cell types about half the time. Current minipromoter systems typically get the proteins in the right place about 5% of the time.
For example, the team injected SLED packages into mice with photoreceptors in the retina that lack a functional PRPH2 gene, which causes retinitis pigmentosa, a form of blindness. The team found evidence that the SLED packages helped produce PRPH2 proteins in the photoreceptors of the treated mice.
The researchers have filed for patents that involve SLED technology. Acccording to Blackshaw, the SLED system’s best potential may be in combination with other gene delivery systems, and his lab is looking into methods to miniaturize introns to accommodate larger-size introns into SLED systems.
Information provided by Johns Hopkins Medicine.