Deploying a method that removes potentially cancer-causing genes, Whitehead Institute researchers have "reprogrammed" human skin cells from Parkinson's disease patients into an embryonic-stem-cell-like state.
Whitehead scientists then used these so-called induced pluripotent stem (iPS) cells to create dopamine-producing neurons, the cell type that degenerates in Parkinson's disease patients.
RELEVANCE: This marks first time researchers have generated human iPS cells, successfully removed the potentially problematic reprogramming genes, and seen the cells maintain their embryonic stem-cell-like state. Previous methods to reprogram mature cells into iPS cells inserted cancer-causing genes into the cells' DNA. Because the current method removes the cancer-causing genes, the resulting iPS cells' DNA is virtually identical to the DNA of the original adult cells. These iPS cells can be matured into any cell type, allowing for screens of potential drug therapies and study of patient-specific disease at the cellular level.
CAMBRIDGE, Mass. (March 5, 2009) – Whitehead Institute researchers have developed a novel method to remove potential cancer-causing genes during the reprogramming of skin cells from Parkinson's disease patients into an embryonic-stem-cell-like state. Scientists then used the resulting induced pluripotent stem (iPS) cells to derive dopamine-producing neurons, the cell type that degenerates in Parkinson's disease patients.
This marks the first time researchers have generated human iPS cells that have maintained their embryonic stem-cell-like properties after the removal of reprogramming genes. The findings are published in the March 6 edition of the journal Cell .
"Until this point, it was not completely clear that when you take out the reprogramming genes from human cells, the reprogrammed cells would actually maintain the iPS state and be self-perpetuating," says Frank Soldner, a postdoctoral researcher in Whitehead Member Rudolf Jaenisch's laboratory and co-author of the article.
Since August 2006, researchers have been reprogramming adult cells into iPS cells by using viruses to transfer four genes (Oct4, Sox2, c-Myc and Klf4) into the cells' DNA. Although necessary for reprogramming cells, these genes, the known oncogene c-Myc in particular, also have the potential to cause cancer. In addition, the four genes interact with approximately 3000 other genes in the cell, which may change how the cell functions. Therefore, leaving the genes behind in successfully reprogrammed cells may cause unintended alterations that limit the cells' applicability for therapeutic use, for drug screens or to study disease in cell culture.
In the current method, Whitehead researchers used viruses to transfer the four reprogramming genes and a gene coding for the enzyme Cre into skin cells from Parkinson's disease patients. The reprogramming genes were bracketed by short DNA sequences, called loxP, which are recognized by the enzyme Cre.
After the skin cells were reprogrammed to iPS cells, the researchers introduced the Cre enzyme into the cells, which removed the DNA between the two loxP sites, thereby deleting the reprogramming genes from the cells. The result is a collection of iPS cells with genomes virtually identical to those of the Parkinson's disease patients from whom original skin cells came.