Induced pluripotent stem cells are made from the adult cells of an individual by means of genetic engineering techniques. After introducing four different genes into adult cells, some of the cells de-differentiate to form cells that grow indefinitely in culture and have most of the characteristics of embryonic stem cells. However, if iPSCs are made from a patient who suffers from a genetic disease, then those stem cells will have the same mutation as the patient, and any derivatives of those iPSCs will show the same behaviors and pathologies of the tissues from the patient. This strategy is called the “disease in a dish” model and it is being increasingly used to make seminal discoveries about diseases and treatment strategies.
Scientists from Cedars-Sinai Regenerative Medicine Institute have used iPSC technology to study Lou Gehrig’s disease, and their research has provided a new approach to treat this horrific, debilitating disease.
Because I have previously written about Lou Gehrig’s disease or Amyotrophic Lateral Sclerosis (ALS), I will not describe it further.
Cedar Sinai scientists isolated skin scrapings from each patient and used the skin fibroblasts from each sample to make iPSCs. According to Dhruv Sareen, the director of the iPSC facility and faculty research scientist with the Department of Biomedical Sciences and the first author on this article, skins cells of patients who have ALS were converted into motor neurons that retained the genetic defects of the disease, thanks to iPSC technology. Then they focused on gene called C9ORF72, which was found to be the most common cause of familial ALS and frontotemporal lobar disease, and is even responsible for some cases of Alzheimer’s and Parkinson’s disease.
Mutations in a gene that has the very non-descriptive name “chromosome 9 open reading frame 72” or C9ORF72 for short seems to play a central role in the onset of Lou Gehrig’s disease. Mutations in C9orf72 have been linked with familial frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). FTD is a brain disorder that typically leads to dementia and sometimes occurs in tandem with ALS.
Mutations in C9ORF72 result from the expansion of a hexanucleotide repeat GGGGCC. When the C9ORF72 gene is replicated, the enzyme that replicates DNA (DNA polymerase) has a tendency to slip when comes to this stretch of nucleotides and this polymerase slip causes the hexanucleotide GGGGCC sequence to wax and wane (expand and shrink). Normally, there are up to 30 repeats of this GGGCC sequence, but in people with mutations in C9ORF72, this GGGGCC repeat can occur many hundreds of times. Massive expansions of the GGGGCC repeat interferes with normal expression of the protein made by C9ORF72. The presence of messenger RNAs (mRNAs) with multiple copies of GGGGCC in the nucleus and cytoplasm is toxic to the cell, since it gums up protein synthesis, RNA processing and other RNA-dependent functions. Also the lack of half of the C9ORF72 protein contributes to the symptoms of this conditions.
Robert Baloh, director of Cedars-Sinai’s Neuromuscular Division and the lead researcher of this research project, said, “We think this buildup of thousands of copies of the repeated sequence GGGGCC in the nucleus of patient’s cells may become toxic by altering the normal behavior of other genes in the motor neurons. Because our studies supported the toxic RNA mechanism theory, we used to small segments of genetic material called antisense oligonucleotides – ASOs – to block the buildup and degrade the toxic RNA. One ASO knocked down overall C9ORF72 levels. The other knocked down the toxic RNA coming from the gene without suppressing overall gene expression levels. The absence of potentially toxic RNA, and no evidence of detrimental effect on the motor neurons, provides a strong basis for using this strategy to treat patients suffering from these diseases.”
Baloh continued: “In a sense, this represents the full spectrum of what we are trying to accomplish with patient-based stem cell modeling. It gives researchers the opportunity to conduct extensive studies of a disease’s genetic and molecular makeup and develop potential treatments in the laboratory before translating them into patient trials.”
Researchers from another institution recently began a phase one clinical trial that used a similar ASO strategy to treat ALS caused by a different mutation. No safety issues were reported in this clinical trial.
Clive Svendsen, director of the Regenerative Medicine Institute and one of the authors, has investigated ALS for more than a decade, said, “ALS may be the cruelest, most severe neurological disease, but I believe the stem cell approach used in this collaborative effort holds the key to unlocking the mysteries of the and other devastating disorders. Within the Regenerative Medicine Institute, we are exploring several other stem cell-based strategies in search of treatments and cures.”
ALS affects 30,000-50,000 people in the US alone, but unlike other neurodegenerative diseases, it is almost always fatal within three to five years.