Every day people flush large quantities of cells down the toilet. We think nothing of it because these cells are sloughed into our urine and there is little that can be done about it. However, Chinese scientists have used cells from urine to make neurons that could eventually be used to treat neurodegenerative diseases.
The technique is described in a study that was published in the journal Nature Methods (Wang, et al., Nature Methods (2012) doi:10.1038/nmeth.2283). Unlike embryonic stem cells, which are derived through the destruction of embryos and have the potential to cause tumors, these neural progenitor cells do not form tumors and are made quickly and without the destruction of human embryos.
Stem cell biology expert Duanqing Pei and his co-workers from China’s Guangzhou Institutes of Biomedicine and Health, which is part of the Chinese Academy of Sciences, previously published a paper that showed that epithelial cells from the kidney that are sloughed into urine can be reprogrammed into induced pluripotent stem cells (iPSCs) (Ting Zhou, et al., Journal of the American Society of Nephrology 2011 vol. 22 no. 7 1221-1228, doi: 10.1681/ASN.2011010106). In this study, Pei and his colleagues used retroviruses to insert pluripotency genes into kidney-based cells to reprogram them. Retroviruses are efficient vectors for genes transfer, but they insert their virus genomes into the genomes of the host cell. This insertion event can cause mutations, and for this reason, retroviral-based introduction of genes into cells are not the preferred way to generate iPSCs for clinical purposes.
Researchers use retroviruses to routinely reprogram cultured skin and blood cells into iPSCs, and these iPSCs can be differentiated into any adult cell type. However, urine is a much more accessible source of cells.
In this present study, Pei’s team used a different technique to introduce genes into the cells from urine; they used “episomal vectors,” which is an overly fancy way of saying that they placed the pluripotency genes on small circles of DNA that were then pushed into the cells. Episomal vectors can reprogram adult cells into iPSCs, but they do so at lower levels of efficiency. Nevertheless, episomal vectors have an added advantage in that the vectors transiently express the pluripotency genes in cells and then are lost without inserting into the host cell genome. This makes episomal vectors inherently safer for clinical purposes.
In one of their experiments, perfectly round colonies of reprogrammed cells from urine that resembled pluripotent stem cells after only 12 days. This is exactly half the time typically required to produce iPSCs. When cultured further, the colonies assumed a rosette shape that is common to neural stem cells.
When Pei and others cultured his urine-derived iPSCs in a culture conditions that normally used for cultured neurons, these cells formed functional neurons in the lab. Could these cells work in the brain of a laboratory animal? Transplantation of these cells into the brains of newborn rats showed that, first of all, they did not form tumors, and, secondly, they took on the shape of mature neurons and expressed the molecular markers of neurons.
The beauty of this experiment is that neural progenitors cells (NPCs) grow in culture and researchers can generate buckets of cells for experiments. However, when cells are directly reprogrammed to neurons, even though they make neurons faster than iPSCs.
James Ellis, a medical geneticist at Toronto’s Hospital for Sick Children in Ontario, Canada who makes patient-specific iPSCs to study autism-spectrum disorders, said: “This could definitely speed things up.”
Another plus of this study is that urine can be collected from nearly any patient and banked to produce instant sources of cells from patients, according to geneticist Marc Lalande, who creates iPSCs to study inherited neurological diseases at the University of Connecticut Health Center in Farmington. Lalande is quite intrigued by the possibility of making iPSCs and NPCs from urine draw from the same patient. Lalande added: “We work on childhood disorders,” he says. “And it’s easier to get a child to give a urine sample than to prick them for blood.”