17 September 2010. One of the three iPSC consortia funded by the National Institute of Neurological Disorders and Stroke (NINDS) is creating lines for amyotrophic lateral sclerosis (ALS). The ALS consortium is headed by Jeff Rothstein at the Robert Packard Center for ALS Research at Johns Hopkins University, Baltimore, Maryland. The scientists are developing iPSC lines for 25 familial forms of ALS, Rothstein said, as well as control lines from healthy people. The Johns Hopkins team will differentiate the iPS cells into astrocytes, while co-PI Chris Henderson at Columbia University, New York, will generate motor neurons from the cells. Two other co-PIs, Tom Maniatis at Columbia and Kevin Eggan at Harvard, will handle iPS cell profiling and biology, Rothstein said.
One of the potential applications of iPSC-derived cells carrying ALS mutations is for drug discovery. However, We don’t know yet if [iPSC-derived cells] will be better than using a rat, Rothstein said. Because it’s faster to use neurons from existing transgenic rat and mouse ALS models than to generate iPS cell lines from humans, Rothstein predicted that rodent cells might remain the method of choice for initial drug screening, with iPSC-derived cells serving a second step of verifying promising drug candidates. The Johns Hopkins team has also generated about 20 lines from sporadic ALS patients, Rothstein said, but these lines are not yet useful as disease models. Rothstein said that is because sporadic ALS cells contain too many unknowns; scientists will need to characterize cells with known mutations before they can make sense of lines from sporadic cases.
For his part, Eggan said that besides his work with the consortia, he also generates his own ALS iPSC lines and has already published several (see ARF related news story on Dimos et al., 2008 and ARF related news story). These lines will be available to other research groups through the iPS Core of the Harvard Stem Cell Institute (HSCI), and many will go online within a few weeks, Eggan said. To date, Eggan and colleagues have made multiple ALS lines from about a dozen patients, including various TDP-43 mutations and an allelic series of SOD1 mutations. His group has also generated control lines from both relatives of patients and unrelated folks. The scientists are using retroviral programming with three factors, a method that Eggan said is almost 100 percent successful in producing iPSC lines from every patient. The lab is currently trying to identify a phenotype in cell cultures made from these iPSC lines, Eggan said. In addition, his lab is working on iPSC lines for the inherited degenerative disease spinal muscular atrophy (SMA), but these lines are not yet ready to distribute.
Neurodevelopmental and Single-Gene Diseases—Voila, a Phenotype!
Monogenetic diseases, such as SMA, are obvious candidates for modeling with iPS cells, because the genetics are simple and the diseases usually manifest earlier. The SMA iPSC line made by first author Allison Ebert, working in Clive Svendsen’s lab at the University of Wisconsin in Madison, has the distinction of being one of the few published iPSC lines to demonstrate a disease phenotype in culture (see Ebert et al., 2008). The published iPS lines were made using a lentiviral vector and reprogramming factors identified by James Thomson at the University of Wisconsin (see Yu et al., 2007). Both the iPS cells and the fibroblasts are available through Coriell Institute for Medical Research in Camden, New Jersey, said Ebert’s colleague Jered McGivern. The lab is currently making additional SMA lines for comparison, McGivern said. The scientists are generating some of the new lines using a non-integrating episomal vector, also developed by Thomson (see Yu et al., 2009).
Induced pluripotent stem cells are particularly valuable for studying SMA, McGivern said, because the disease only occurs in humans. There are some model systems in mice, but they may not recapitulate what happens in humans, he added. McGivern said the lab also has some Huntington disease-specific iPSC lines that were made with fibroblasts from Coriell and reprogrammed in the Thomson lab.
Other published iPSC lines for monogenetic and neurodevelopmental diseases include a fragile X iPSC line created by researchers working with George Daley at Harvard (see Urbach et al., 2010). There is also an iPSC line for familial dysautonomia—an inherited disorder in which autonomic and sensory nerves malfunction—made by researchers led by Lorenz Studer at Sloan-Kettering Institute in New York (see Lee et al., 2009). The familial dysautonomia line has shown a disease phenotype in culture. James Ellis’s group at the University of Toronto, Canada, published an iPSC line from a Rett syndrome patient (see Hotta et al., 2009). Ellis said he is currently collecting biopsies from patients in his pediatric clinic, and using them to generate more iPSC lines for neurodevelopmental disorders such as Rett syndrome, autism, and schizophrenia, as well as making control lines from relatives of patients. These lines will initially be available from Ellis, later through the Ontario Human Induced Pluripotent Stem Cell Facility.
To use all of these disease-specific iPSC lines for disease modeling, researchers will also need control lines from healthy people. Most research groups are making their own control lines from relatives of patients, but some lines are also commercially available, or will be soon. The stem cell bank at the University of Wisconsin in Madison, WiCell, stocks several iPSC lines made by Thomson using both lentiviral and episomal vectors.
Coriell, a nonprofit biomedical research institution, not only banks iPSC lines from many other labs, but is also developing its own lines. At the moment, Coriell is focusing on making iPSC lines from fibroblasts taken from healthy people, Margaret Keller, director of Coriell’s stem cell bank, wrote to ARF; future plans include making iPSC lines from people with diseases. This work, which is sponsored by the National Institute of General Medical Sciences (NIGMS), currently uses a lentiviral reprogramming protocol based on the one developed by Thomson, Keller said, though they may also use a non-viral method in the future. Coriell will make both the iPSC lines and fibroblasts available to researchers, with the first lines predicted to come online in late 2010, Keller said. Coriell also banks numerous lines from other researchers, many of which are expected to become available through the NIGMS Repository collection in late 2010.
Clearly, there will soon be numerous cell lines available for researchers interested in studying neurodegenerative diseases with iPS cells. This brings to the fore a question that has been lurking just beneath all this effort. How useful are these lines as disease models What limitations should researchers keep in mind For an answer to these questions, come back for upcoming Part 4 of this series.
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