STAP Cells: Stress-Induced Stem Cells?
The findings of researcher claiming to have developed a new method to reprogram differentiated cells into pluripotent, and even totipotent, stem cells have been brought into question by allegations of misconduct. The group behind these papers, from the RIKEN Center for Developmental Biology (Japan), reported using an acid bath and other external environmental stresses to revert a variety of somatic mouse cells into stimulus-triggered acquisition of pluripotency (STAP) cells. The findings caused great excitement; however, a number of serious concerns have been raised regarding the papers.
When these issues came to light, some coauthors of the papers called for the article to be retracted, however, lead author Haruko Obokata claims that these issues do not impact the validity of the findings and maintains that STAP cells are real. Due to the seriousness of the allegations RIKEN conducted an investigation into the research and the papers, the findings of which were published in early April.
The RIKEN investigation found that Obokata had engaged in two instances of “research misconduct” and manipulated the image data for one of the figures. Three other coauthors were identified as being “gravely responsible” for failing to fully verify the research findings. Obokata has appealed against the investigation report.
Obokata, a stem cell biologist at the RIKEN Center, noticed that some somatic cells woudl have similar characteristics to stem cells after they had been forced through a capillary tube. Obokata decided to see if other stresses, including heat, starvation and a high-calcium environment, would have the same effect. After being exposed to three particular stresses – a bacterial toxin, low level acid and physical squeezing – somatic cells showed signs of pluripotency. “It’s amazing. I would never have thought external stress could have this effect,” said Yoshiki Sasai, a stem cell researcher at the RIKEN Center for Developmental Biology and a coauthor of the articles.
According to the disputed papers, the blood cells of 1-week-old mice were exposed to these stresses, tagged with GFP and then injected into mouse embryos to produce fully fluorescent green embryos; the authors suggested that this shows the cells had acquired full pluripotency. Obokata continued her experiments to try and show that brain, skin, lung and liver cells could be reprogrammed using these stresses.
If proven, STAP cells would be similar to the induced pluripotent stem (iPS) cells that were developed by Shinya Yamanaka, Kyoto University (Japan), in 2006. However, the method to make iPS cells is time-consuming as it requires the activation of a number of pluripotent genes. Obokata claimed that on average 25% of somatic cells survive being exposed to the environmental stresses and of those 30% were converted to pluripotent cells; suggesting a conversion rate of 7.5%.
The group published a second paper in the same issue of Nature, claiming that STAP cells can also contribute to the placental tissue. This would demonstrate that STAP cells are not just pluripotent but also totipotent, unlike embryonic and iPS cells.
It is not understood how these environmental stresses supposedly induce pluripotency in cells; however, Charles Vacanti, Harvard University (MA, USA) and lead author of one of the papers, suggested that “the generation of these cells is essentially Motehr Nature”s way of responding to injury.”
A number of issues with the papers were raised in the weeks after publication. The most major of which were:
| • | A figure showing genetic changes in the reprogrammed cells appeared to have been doctored; | ||||
| • | A section of text that describes the methods for examining chromosomes seemed to have been copied from a previously published paper; | ||||
| • | The same methods appeared to have not been followed correctly in them experiments; | ||||
| • | A figure of a mouse that was reportedly developed from STAP cells looked similar to a figure of a mouse from Obokata’s 2011 doctoral thesis. | ||||
These issues, combined with other laboratories’ inability to replicate the protocol, meant that the papers and the existence of STAP cells were cast into doubt. Following the finding of research misconduct by the RIKEN center, Harvard and Nature are currently conducting their own investigations.
This article was updated on the 24th April 2014
Sources: Obokata H, Wakayama T, Sasai Y et al. Stimulus-triggered fate conversion of somatic cells into pluripotency. Nature 505, 641–647 (2014); Obokata H, Sasai Y, Niwa H et al. Bidirectional developmental potential in reprogrammed cells with acquired pluripotency. Nature 505, 676–680 (2014); Nature news: www.nature.com/news/acid-bath-offers-easy-path-to-stem-cells-1.14600#/b3; Knoepfler Lab Stem Cell Blog: www.ipscell.com/2014/01/review-of-obokata-stress-reprogramming-nature-papers
Baldly Going where no Stem Cell Scientist has gone Before
A group from the University of Pennsylvania (PA, USA) has published a study that demonstrates the differentiation of human induced pluripotent stem cells (hiPSCs) into a large number of folliculogenic epithelial stem cells (EpSCs) in a recent issue of Nature Communication. It is hoped this could be used as a treatment for baldness.
The investigators began by converting dermal fibroblast skin cells into hiPSCs by activating three pluripotent genes. These cells were then differentiated into keratinocyte EpSCs, which are normally found at the bulge of hair follicles. The hiPSC-dervied EpSCs showed a similar gene expression signature as EpSCs directly isolated from human hair follicles and the cells reconstituted the epithelial components of the hair follicle and interfollicular epidermis. Using skin reconstitution assays, it was shown that the hiPSC-derived EpSCs were capable of generating all hair follicle lineages including the hair shaft, and the inner and outer root sheaths.
The University of Pennsylvania investigators used previously published protocols to differentiate hiPSCs nto keratinocytes; however, the group made adjustments to the timing that the growth factors were introduced. These alterations meant the hiPSCs generated large numbers of EpSCs, with a successful conversion rate of 25% over 18 days.
Xiaowei Xu, Professor of Pathology and Laboratory Medicine at the Perelman School of Medicine, University of Pennsylvania, said: “This is the first time anyone has made scalable amounts of EpSCs that are capable of generating the epithelial component of hair follicles.”
“When a person loses hair, they lose both types of cells,” Xu explained. “We have solved one major problem, the epithelial component of the hair follicle. We need to figure out a way to also make new dermal papillae cells, and no one has figured that part out yet.”
Sources: Yang R, Zheng Y, Burrows M et al. Generation of folliculogenic human epithelial stem cells from induced pluripotent stem cells. Nat. Commun. 5, 3071 (2014); University of Pennsylvania press release: www.upenn.edu/pennnews/news/penn-medicine-first-study-convert-adult-human-cells-hair-follicle-generating-stem-cells-has-imp
Successful Differentiation of Human Pluripotent Stem Cells into Endoderm
New research published in a recent issue of Cell Stem Cell has shown the efficient differentiation of human pluripotent stem cells (hPSCs) into endodermal cells. This study was carried out by investigators at the Genome Institute of Singapore (GIS; Singapore) who hope this development will further the research of liver and pancreas regeneration.
Historically, it has been difficult for stem cell scientists to differentiate endodermal cells from hPSCs, however, this newly developed ‘signaling roadmap‘ can efficiently produce pure endoderm populations at higher yields from hPSCs. The GIS investigators began by identifying proteins and chemicals that induced endodermal differentiation in hPSCs. However, in order to produce pure populations of endodermal cells, the group also had to block any other external signals that would produce unwanted cell types in the colony. They found that the BMP and Wnt pathways originally start to induce endodermal differentiate via the primitive streak; however, the same pathways suppressed endoderm and induced mesoderm later in development.
Professor Thomas Graf, coordinator of the Differentiation and Cancer Programme at the Center for Genomic Regulation (Barcelona, Spain), commented: “Using this novel strategy, the work beautifully shows how hPSCs can be guided to differentiate into the endoderm cells at high efficiencies. The strategy described should be more widely applicable to other desired cell types.”
Once endodermal progenitor cells have been induced, activating the TGF-β and BMP/MAPK pathways in the cells produced pancreas and liver tissue, respectively. Dr Bing Lim, senior group leader and Associate Director of Cancer Stem Cell Biology at the GIS, explained: “This unprecedented access to highly pure population of endodermal cells attracts pharmaceutical companies, who are interested in further making human liver cells to tests drug toxicities.”
Dr Shyam Prabhakar, group leader of computational and systems biology, and Associate Director of Integrative Genomics at the GIS, said: “Our new results indicate that the reality is more complex. Beyond current scientific knowledge, we found a larger superset of inactive enhancer states, all of which have the ability to convert to an active state upon cell differentiation.”
Huck Hui Ng, Executive Director of the GIS, concluded: “This is a beautiful piece of work to delineate the early events in cell fate decision. The findings will enable researchers to obtain high quality endodermal cells for future applications.”
Sources: Loh KM, Ang LT, Zhang J et al. Efficient endoderm induction from human pluripotent stem cells by logically directing signals controlling lineage bifurcations. Cell Stem Cell doi:10.1016/j.stem.2013.12.007 (2014) (Epub ahead of print); Genome Institute of Singapore press release: www.a-star.edu.sg/Media/News/Press-Releases/articleType/ArticleView/articleId/1988.aspx
– All stories written by Theo Bond