Stem cells have the unique ability to become any type of cell in the body. Given this, the possibility that they can be cultured and engineered in the laboratory makes them an attractive option for regenerative medicine. However, some conditions that are commonly used for culturing human stem cells have the potential to introduce contaminants, thus rendering the cells unusable for clinical use. These conditions cannot be avoided, however, as they help maintain the pluripotency of the stem cells.

In a study published in Scientific Reports, a group from the RIKEN Center for Life Science Technologies in Japan has gained new insight into the role of CCL2, a chemokine known to be involved in the immune response, in the enhancement of stem cell pluripotency. In the study, the researchers replaced basic fibroblast growth factor (bFGF), a critical component of human stem cell culture, with CCL2 and studied its effect. The work showed that CCL2 used as a replacement for bFGF activated the JAK/STAT pathway, which is known to be involved in the immune response and maintenance of mouse pluripotent stem cells. In addition, the cells cultured with CCL2 demonstrated a higher tendency of colony attachment, high efficiency of cellular differentiation, and hints of X chromosome reactivation in female cells, all markers of pluripotency.

To understand the global effects of CCL2, the researchers compared the transcriptome of stem cells cultured with CCL2 and those with bFGF. They found that stem cells cultured with CCL2 had higher expression of genes related to the hypoxic response, such as HIF2A (EPAS1). The study opens up avenues for further exploring the relationship between cellular stress, such as hypoxia, and the enhancement of pluripotency in cells. Yuki Hasegawa of CLST, who led the study, says, "Among the differentially expressed genes, we found out that the most significantly differentially expressed ones were those related to hypoxic responses, and hypoxia is known to be important in the progression of tumors and the maintenance of pluripotency. These results could potentially contribute to greater consistency of human induced pluripotent stem cells (iPSCs), which are important both for regenerative medicine and for research into diseases processes."

As a way to apply CCL2 towards the culturing of human iPSCs with more consistent quality, the researchers developed dishes coated with CCL2 and LIF protein beads. This allowed stem cells to be cultured in a feeder-free condition, preventing the risk that viruses or other contaminants could be transmitted to the stem cells. While the exact mechanisms of how CCL2 enhances pluripotency has yet to be elucidated, this work highlights the usefulness of CCL2 in stem cell culture.

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The above story is based on materials provided by RIKEN. Note: Materials may be edited for content and length.

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Pushing cells towards a higher pluripotency state

PUBLIC RELEASE DATE:

19-Jun-2014

Contact: Mary Beth O'Leary moleary@cell.com 617-397-2802 Cell Press

Stroke is a leading cause of death and disability in developed countries, and there is an urgent need for more clinically effective treatments. A study published by Cell Press June 19th in Stem Cell Reports reveals that simultaneous transplantation of neural and vascular progenitor cells can reduce stroke-related brain damage and improve behavioral recovery in rodents. The stem cell-based approach could represent a promising strategy for the treatment of stroke in humans.

"Our findings suggest that early cotransplantation treatment can not only replace lost cells, but also prevent further deterioration of the injured brain following ischemic stroke," says senior study author Wei-Qiang Gao of Shanghai Jiaotong University. "With the development of human embryonic and induced pluripotent stem cell technology, we are optimistic about the potential translation of our research into clinical use."

The most common kind of stroke, known as ischemic stroke, is caused by a blood clot that blocks or plugs a blood vessel in the brain. Although a medicine called tissue plasminogen activator can break up blood clots in the brain, it must be given soon after the start of symptoms to work, and there are no other clinically effective treatments currently available for this condition. Stem cell transplantation represents a promising therapeutic strategy, but transplantation of either neural progenitor cells or vascular cells has shown restricted therapeutic effectiveness.

In the new study, Gao teamed up with colleagues at Shanghai Jiao Tong University, including Jia Li, Yaohui Tang, and Guo-Yuan Yang, to test whether cotransplantation of both neural and vascular precursor cells would lead to better outcomes. They induced ischemic stroke in rats and then simultaneously injected neural and vascular progenitor cells from mice into the stroke-damaged rat brains 24 hours later. The transplanted precursor cells turned into all major types of vascular and brain cells, including mature, functional neurons. The resulting vascular cells developed into microvessels, while the grafted neural cells produced molecules known to stimulate the growth of both neurons and vessels.

"This is the first study to use embryonic stem cell-derived vascular progenitor cells together with neural progenitor cells to treat ischemic stroke," Gao says. "These two types of progenitors generate nearly all types of brain cells, including endothelial cells, pericytes/smooth muscle cells, neurons, and astrocytes, resulting in better restoration of neurovascular units and better replacement of the lost cells in the stroke model. A previously reported cotransplantation approach published in the journal Stem Cells in 2009 (doi: 10.1002/stem.161) was limited because it did not use vascular precursor cells capable of turning into all major types of vascular cells important for recovery. Our findings here suggest that cotransplantation of the two types of cells that restore the neurovascular unit more effectively is a better approach for the treatment of ischemic stroke."

Two weeks after stroke, rats that had undergone cotransplantation showed less brain damage and improved behavioral performance on motor tasks compared with rats that had been treated with neural progenitor cells alone. "Our findings suggest that cotransplantation of neural and vascular cells is much more effective than transplantation of one cell type alone because these two cell types mutually support each other to promote recovery after stroke," Gao says.

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Stem cell-based transplantation approach improves recovery from stroke

PUBLIC RELEASE DATE:

12-Jun-2014

Contact: Hannah Postles h.postles@sheffield.ac.uk 01-142-221-046 University of Sheffield

A time-lapse study of human embryonic stems cells has identified bottlenecks restricting the formation of colonies, a discovery that could lead to improvement in their use in regenerative medicine.

Biologists at the University of Sheffield's Centre for Stem Cell Biology led by Professor Peter Andrews and engineers in the Complex Systems and Signal Processing Group led by Professor Daniel Coca studied human pluripotent stem cells, which are a potential source of cells for regenerative medicine because they have the ability to produce any cell type in the body.

However, using these stem cells in therapies is currently hampered by the fact they can acquire genetic changes during prolonged culture which are non-random and resemble mutations in cancer cells.

Researchers used time-lapse imaging of single human embryonic stem cells to identify aspects of their behaviour that restrict growth and would be targets for mutations that allow cells to grow more efficiently.

Dr Ivana Barbaric, from the University of Sheffield's Department of Biomedical Science, said: "We study pluripotent stem cells, which have huge potential for use in regenerative medicine due to their ability to become any cell in the human body. A pre-requisite for this is maintaining large numbers of undifferentiated cells in culture. However, there are several obstacles such as cells tend to die extensively during culturing and they can mutate spontaneously. Some of these genetic mutations are known to provide stem cells with superior growth, allowing them to overtake the culture a phenomenon termed culture adaptation, which mimics the behaviour of cancer cells.

"In order for pluripotent stem cells to be used safely in regenerative medicine we need to understand how suboptimal culture conditions, for example culturing cells at low split ratios, affect the cells and can lead to culture adaptation."

The team's research combined the use of time-lapse microscopy, single-cell tracking and mathematical modelling to characterise bottlenecks affecting the survival of normal human embryonic stem cells and compared them with adapted cells.

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Time-lapse study reveals bottlenecks in stem cell expansion