Editing scrambled genes in human stem cells may help realize the promise of stem cell-gene therapy

May 19, 2011

In principle, genetic engineering is simple, but in practice, replacing a faulty gene with a healthy copy is anything but. Using mutated versions of the lamin A gene as an example to demonstrate the versatility of their virus-based approach, researchers at the Salk Institute for Biological Studies successfully edited a diseased gene in patient-specific induced pluripotent stem cells as well as adult stem cells.

The study, which will be published in the June 3, 2011 issue of Cell Stem Cell but are already available online, demonstrates that the gene-editing approach developed by Salk professor Juan Carlos Izpisúa Belmonte, Ph.D., and his team provides an efficient and safe tool for cell engineering and opens the way for gene editing-based stem cell therapies suitable for clinical applications.

"The ability to derive and grow human in the laboratory has raised enormous expectations within the biomedical community due to their transplantational potential in clinical settings," says Izpisua Belmonte, a professor in the Gene Expression Laboratory and the study's leader. "This, when combined with the development of efficient and safe gene editing technologies in human stem cells may greatly help the realization of these expectations."

As envisioned by its earliest proponents, gene therapy introduces a healthy copy of a gene to compensate for a defective one in the patient. But that approach has a major drawback. "Many therapeutic are only expressed transiently before they get shut off by the host cell or they are not expressed as expected because they don't occupy the same position in the genome as the natural genes," explains postdoctoral researcher and co-first author Keiichiro Suzuki.

To overcome those limitation, over the last several years, scientists tried to develop methods that allow them to precisely excise the section of the genome that encompasses the mutated gene and replace it with a matching fragment but sans mutation. One such method relies on molecular "fingers" that grab onto DNA, make a cut and stitch in the new sequence.

"There are still some unresolved problems with the so-called zinc-finger method," says postdoctoral researcher and co-first author Guang-Hui Liu. "The tricky part is to limit the zinc fingers to the sequence you are interested in to avoid introducing DNA breaks or new mutations elsewhere in the genome."

The Salk researchers addressed the shortcomings of previously established methods by taking advantage of an iPS-based model of Hutchinson-Gilford progeria, which was recently established in the laboratory of Izpisúa Belmonte. A rare, premature aging disease, Hutchinson-Gilford progeria is caused by a single point mutation in the gene encoding lamin A, which forms a protein scaffold on the inner edge of the nucleus that helps maintain chromatin structure and organize nuclear processes such as RNA and DNA synthesis.

Importantly, more that 400 different mutations in the lamin A gene have been reported, which are associated with a wide range of human degenerative diseases including muscular dystrophy, lipodystrophies and neuropathies.

The gene-targeting approach developed by Suzuki and his colleagues relies on the use of so-called helper-dependent adenoviral vector to deliver large mutation-free DNA molecules into cells. Once there, these replacement pieces initiate a process known as homologous recombination, which works a bit like the "find-and-replace" command in a word processor. If a piece of DNA is long enough, it will find and line up with the same sequence in the genome and swap places.

"The process was remarkably efficient and we couldn't detect any undesired off-target effects such genomic instability or epigenetic abnormalities," says Liu. "What's more, it allowed us to show that we can correct multiple mutations spanning large genomic regions."

In addition to iPS cells derived from progeria-patients, the researchers successfully applied their method to adult mesenchymal stem cells, which can differentiate into a variety of cell types, including adipocytes, osteoblasts, chondrocytes, cardiomyocytes, adipocytes, and, as described lately, beta-pancreatic islets cells.

"As a proof of principle, we focused on mesenchymal because of their extensive use in regenerative medicine," says Izpisúa Belmonte. "Lamin A mutations mainly effect mesoderm-derived tissues, thus gene-editing in these cells could be an attractive therapeutic option."

Explore further: Life's extremists may be an untapped source of antibacterial drugs

Related Stories

Aging, interrupted (w/ Video)

Feb 23, 2011

The current pace of population aging is without parallel in human history but surprisingly little is known about the human aging process, because lifespans of eight decades or more make it difficult to study. ...

Researchers edit genes in human stem cells

Jun 18, 2009

Researchers at the Johns Hopkins School of Medicine have successfully edited the genome of human- induced pluripotent stem cells, making possible the future development of patient-specific stem cell therapies. Reporting this ...

Uncovering the trail behind growing too old, too soon

Jan 24, 2011

Scientists from A*STAR's Institute of Medical Biology (IMB) in Singapore and the University of Hong Kong's Department of Medicine have produced the world's first human cell model of progeria, a disease resulting in severe ...

A fly lamin gene is both like and unlike human genes

Jun 13, 2007

Mitch Dushay and colleagues at Uppsala University in Sweden announce the publication of their paper, "Characterization of lamin Mutation Phenotypes in Drosophila and Comparison to Human Laminopathies" in the June 13th issue ...

Recommended for you

Cohesin molecule safeguards cell division

Nov 21, 2014

The cohesin molecule ensures the proper distribution of DNA during cell division. Scientists at the Research Institute of Molecular Pathology (IMP) in Vienna can now prove the concept of its carabiner-like ...

Nail stem cells prove more versatile than press ons

Nov 21, 2014

There are plenty of body parts that don't grow back when you lose them. Nails are an exception, and a new study published in the Proceedings of the National Academy of Sciences (PNAS) reveals some of the r ...

Scientists develop 3-D model of regulator protein bax

Nov 21, 2014

Scientists at Freie Universität Berlin, the University of Tubingen, and the Swiss Federal Institute of Technology in Zurich (ETH) provide a new 3D model of the protein Bax, a key regulator of cell death. When active, Bax ...

Researchers unwind the mysteries of the cellular clock

Nov 20, 2014

Human existence is basically circadian. Most of us wake in the morning, sleep in the evening, and eat in between. Body temperature, metabolism, and hormone levels all fluctuate throughout the day, and it ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.