The Pluripotent

The reprogramming field seems to be moving oh-so-fast.  First authorJian-Chien Dominic Heng (Genome Institute of Singapore) and colleagues in Singapore and Boston have discovered that a nuclear receptor known as Nr5a2 or Lrh-1 can replace Oct4, a critical transcription factor thought to be needed for generating induced pluripotent stem (iPS) cells.  This discovery adds another question to the current putative models to what molecular mechanisms are involved when a somatic cell is reprogrammed the the pluripotent state. It’s possible that Nr5a2, which has a multitude of biological functions,  has similar functions or binding sites as Oct4.  It’s also possible that Nr5a2 a direct target of Oct4 and has always been a critical factor in the reprogramming program. Nr5a2, who are you?

Here’s the abstract:

Somatic cells can be reprogrammed to induced pluripotent stem cells (iPSCs) with the introduction of Oct4, Sox2, Klf4, and c-Myc. Among these four factors, Oct4 is critical in inducing pluripotency because no transcription factor can substitute for Oct4, whereas Sox2, Klf4, and c-Myc can be replaced by other factors. Here we show that the orphan nuclear receptor Nr5a2 (also known as Lrh-1) can replace Oct4 in the derivation of iPSCs from mouse somatic cells, and it can also enhance reprogramming efficiency. Sumoylation mutants of Nr5a2 with enhanced transcriptional activity can further increase reprogramming efficiency. Genome-wide location analysis reveals that Nr5a2 shares many common gene targets with Sox2 and Klf4, which suggests that the transcription factor trio works in concert to mediate reprogramming. We also show that Nr5a2 works in part through activating Nanog. Together, we show that unrelated transcription factors can replace Oct4 and uncovers an exogenous Oct4-free reprogramming code.

Have access to Cell Stem Cell? Get the paper here.

Popularity: 10% [?]

According to the WHO, there aren’t any treatments to reverse the disability caused by strokes, which occur when there is a sudden loss of blood to the brain. And every year, about 5 million people worldwide are disabled by strokes.

After multiple failures from getting permission from U.S. regulators, ReNeuron Group Plc is performing a study in the U.K. with fetal brain cells on stroke victims. A neurosurgeon at Southern General Hospital in Glasgow, Scotland, plans to drill a hole in a patient’s skull, insert a needle and inject 2 million stem cells from ReNeuron into his brain next year. The patient is the first of 12 men disabled by strokes who expect to receive from these cells grown from the brain of an aborted 12-week-old fetus. The men would be studied for two years to see if the cells help the brain repair damage without causing further harm. Several other biotech representatives are not confident in this study.

[Via Bloomberg]

Popularity: 9% [?]

Research led by Dr. Steven McKnight of UT Southwestern Medical Center has demonstrated that the activation of a particular gene encoding threonine dehydrogenase (TDH) may be a key component of why mouse embryonic stem cells are easily grown in a laboratory while other mammalian ES cells are difficult, if not impossible, to maintain.

Here’s the abstract:

Measurements of the abundance of common metabolites in cultured embryonic stem (ES) cells revealed an unusual state with respect to one-carbon metabolism. These findings led to the discovery of copious expression of the gene encoding threonine dehydrogenase (TDH) in ES cells. TDH-mediated catabolism of threonine takes place in mitochondria to generate glycine and acetyl-CoA, with glycine facilitating one-carbon metabolism via the glycine cleavage system and acetyl-CoA feeding the tricarboxcylic acid (TCA) cycle. Culture media individually deprived of each of the 20 amino acids were applied to ES cells, leading to the discovery that ES cells are critically dependent upon but one amino acid—threonine. These observations show that ES cells exist in a unique, high-flux backbone metabolic state comparable to that of rapidly growing bacterial cells.

Get the full text here (with access).

Popularity: 14% [?]

The Anatomy of A Silent Crisis

It cannot be denied that global warming has made its presence more visible each year. The rise in temperatures   threaten the lifestyles of not only animals but humans as well.  As animals are forced to adapt to changing habitats, only the most adaptable will survive. This applies to humans as well.  The simple rise in temperature has acted as a domino effect in which the consequences are being discovered daily.

Most recently it has been reported that this climate change has led to  300,000 deaths and about $125 billion in economic losses as reported by the Global Humanitarian Forum. Along with the deaths, the report said that the lives of 325 million people, primarily in poor countries, were being seriously affected by climate change. It projected that the number would double by 2030. Although a few experts question the methodology and conclusion of the report, the Global Humanitarian Forum defends their report by saying that it serves merely as an estimate. Its real goal seems to be is to draw political and public awareness to a rising problem.

Although global warming has played a part in the economies of these denizens, this report has brought to light the more apparent need. The need to accommodate governmental policies  in order to reduce the vulnerability in dealing with global warming. We are the ones who need to adapt in order to be those that can survive.

via [NYT]

Popularity: 18% [?]

Hwang Woo-suk’s Sooam Biotech Research Center has claimed they have for the first time created cloned pig embryos and used them to make embryonic stem-cell lines.  If you’ve been living in a cave (or a lab) during 2004, Hwang is the man who claimed to have succeeded in cloning human embryos by nuclear transfer.  After much excitement for his alleged results, it all turned about to be quacky, sending Hwang’s reputation down to hell.

Hyun Sang-hwan, Hwang’s key colleague at Sooam, told The Korea Times that the study will be reported in Zygote, a peer-review journal published by Cambridge University, in two or three months. Hyun also said the study on cloned pig stem cells will mark the starting point of Hwang’s comeback.

Let’s just see how reproducible the data will be.

[Via The Korea Times]

Popularity: 12% [?]

Anjali Nayar reports that a gene on the extra chromosome that causes Down’s syndrome helps to protect those with the disorder from some types of cancer. Sandra Ryeom, a vascular biologist at Children’s Hospital Boston in Massachusetts, and her colleagues experimented with mice and with human cells to show that an additional third copy of the DSCR1 gene (also known as RCAN1) can suppress the growth of the blood vessels that feed cancerous tumours.  The paper by Baek, K.-H. et al. is in Nature’s advance online publication.

[Via Nature]

Popularity: 24% [?]

Monya Baker of Nature Stem Cells has written a feature addressing some of the most important questions about iPS cells.  Here’s her introductory paragraph under iPS cell mysteries:

“Induced pluripotent stem (iPS) cells have been minutely studied ever since their invention, but their fundamentals are still mysterious. How similar are they to ES cells? Will specialized cells generated from them adequately represent disease? Perhaps the key to answering these practical questions is the two most fundamental mysteries of all: how is it possible to turn a differentiated cell into a pluripotent one, and what is the pluripotent state?”

Read the full text here.

Popularity: 7% [?]

Here’s some exciting news regarding hematopoietic stem cell development coming from Boston (The Pluripotent headquarters).  Two studies by Leonard Zon’s and George Daley’s groups have supported the following hypothesis:  A beating heart and blood flow are necessary for development of the blood system, which relies on mechanical stresses to cue its formation.

Zon and colleagues found that compounds that modulate blood flow had a potent impact on the expression of a Runx1, a master regulator of blood formation.  Runx1 is also a recognized marker for the blood stem cells that give rise to all the cell types in the blood system.  They also observed that a strain of mutant embryos that lacked a heartbeat and blood circulation exhibited severely reduced numbers of blood stem cells.  And the key biochemical regulator that was in charge of all this?  Nitric oxide!  Increasing nitric oxide in the blood of mutant embryos rescued blood stem cell production.

Daley and colleagues discovered that just the stress and biomechanical forces on the lining of blood vessels were able to increase the production of progenitor cells that gave rise to blood cells.

The report by Children’s Hospital says “the authors of the two papers speculate that drugs that mimic the effects of embryonic blood flow on blood precursor cells, or molecules involved in nitric oxide signaling, might be therapeutically beneficial for patients with blood diseases. For example, nitric oxide could be used to grow and expand blood stem cells either in the culture dish or in patients after transplantation.”

Anyone up for testing nitric oxide for blood doping?  On second thought, please don’t try it.

Abstracts:

Zon:

During vertebrate embryogenesis, hematopoietic stem cells (HSCs) arise in the aorta-gonads-mesonephros (AGM) region. We report here that blood flow is a conserved regulator of HSC formation. In zebrafish, chemical blood flow modulators regulated HSC development, and silent heart (sih) embryos, lacking a heartbeat and blood circulation, exhibited severely reduced HSCs. Flow-modifying compounds primarily affected HSC induction after the onset of heartbeat; however, nitric oxide (NO) donors regulated HSC number even when treatment occurred before the initiation of circulation, and rescued HSCs in sih mutants. Morpholino knockdown of nos1 (nnos/enos) blocked HSC development, and its requirement was shown to be cell autonomous. In the mouse, Nos3 (eNos) was expressed in HSCs in the AGM. Intrauterine Nos inhibition or embryonic Nos3 deficiency resulted in a reduction of hematopoietic clusters and transplantable murine HSCs. This work links blood flow to AGM hematopoiesis and identifies NO as a conserved downstream regulator of HSC development.

Full text

Daley:

Biomechanical forces are emerging as critical regulators of embryogenesis, particularly in the developing cardiovascular system^{1, 2}. After initiation of the heartbeat in vertebrates, cells lining the ventral aspect of the dorsal aorta, the placental vessels, and the umbilical and vitelline arteries initiate expression of the transcription factor Runx1 (refs 3–5), a master regulator of haematopoiesis, and give rise to haematopoietic cells⁴. It remains unknown whether the biomechanical forces imposed on the vascular wall at this developmental stage act as a determinant of haematopoietic potential⁶. Here, using mouse embryonic stem cells differentiated in vitro, we show that fluid shear stress increases the expression of Runx1 in CD41⁺c-Kit⁺ haematopoietic progenitor cells⁷, concomitantly augmenting their haematopoietic colony-forming potential. Moreover, we find that shear stress increases haematopoietic colony-forming potential and expression of haematopoietic markers in the para-aortic splanchnopleura/aorta–gonads–mesonephros of mouse embryos and that abrogation of nitric oxide, a mediator of shear-stress-induced signalling⁸, compromises haematopoietic potential in vitro and in vivo. Collectively, these data reveal a critical role for biomechanical forces in haematopoietic development.

Full text

[Via CHB]

Popularity: 10% [?]

Todd Ransom of UC Riverside reports:

A new development in stem cell research has resulted from a completed study by a collaboration of scientists using the drug Rapamycin to inhibit mTOR, an intracellular protein necessary in cell proliferation. UCR’s Jiayu Liao, assistant professor in the Department of Bioengineering at Bourns College of Engineering, recently published a paper on the results in the Proceeding of the National Academy of Sciences dealing with human embryonic stem cell pluripotency.

His team inhibited mTOR using Rapamycin, a drug approved by the Food and Drug Administration, and found that pluripotency (the ability to create all cell types) was impaired, stem cell self-renew was prevented, and endodermal and mesodermal differentiation were enhanced.

“Stem cells can potentially develop into cancer,” Liao said. “That’s why it is important to be certain that any stem cells introduced into patients do not remain pluripotent, which has the potential to form tumors. The use of Rapamycin could potentially prevent this problem.”

Stem cells can differentiate into and of the three germ layers: the endoderm (interior stomach lining, gastrointestinal tract, the lungs), the mesoderm (muscle, bone, blood, urogenital), or the ectoderm (epidermal tissues and nervous system). Pluripotent stem cells can give rise to any fetal or adult cell type. However, alone they cannot develop into a fetal or adult animal because they lack the potential to contribute to extra embryonic tissue, such as the placenta.

“You don’t want to maintain pluropotency when using stem cells for treatment,” Liao said. “You want them all to differentiate into one of the three germ layers.”

The discovery could have a significant impact on the future use of stem cells in regenerative medicine, he added. Rapamycin itself is also an immunosuppressant which prevents rejection of organ transplantation from the host.

“It really opens the door for stem cell research towards translational medicine” he said.

In addition, because the drug is FDA approved, there is no need to order clinical trials for safety so the method can be placed into treatment immediately.

Here’s the abstract:

“Despite the recent identification of the transcriptional regulatory circuitry involving SOX2, NANOG, and OCT-4, the intracellular signaling networks that control pluripotency of human embryonic stem cells (hESCs) remain largely undefined. Here, we demonstrate an essential role for the serine/threonine protein kinase mammalian target of rapamycin (mTOR) in regulating hESC long-term undifferentiated growth. Inhibition of mTOR impairs pluripotency, prevents cell proliferation, and enhances mesoderm and endoderm activities in hESCs. At the molecular level, mTOR integrates signals from extrinsic pluripotency-supporting factors and represses the transcriptional activities of a subset of developmental and growth-inhibitory genes, as revealed by genome-wide microarray analyses. Repression of the developmental genes by mTOR is necessary for the maintenance of hESC pluripotency. These results uncover a novel signaling mechanism by which mTOR controls fate decisions in hESCs. Our findings may contribute to effective strategies for tissue repair and regeneration.”

Get the full text here (access required).

[Via UC Riverside PR]

Popularity: 5% [?]

Linda Hemphill reports on the 87th General Session of the International Association for Dental Research:

Human embryonic stem cells (hESC) provide a potentially unlimited source of oral mucosal tissues that may revolutionize the treatment of oral diseases. When fully exploited in the future, this source of cells will be able to produce functional tissues to treat a broad variety of oral diseases. However, little is known about how hESC can be developed into complex, multilayer oral tissues that line the gums, cheeks, lips, and other intra-oral sites. However, the use of hES cells for oral application faces numerous obstacles that must be overcome before their therapeutic potential can be realized.

During the 87th General Session of the International Association for Dental Research, investigators from Tufts University in Boston report on their research to optimize the potential of hESC cells to generate complex, functional multilayer tissues, such as the oral mucosa and skin, and to understand how tissue fabrication is controlled and directed.

The Garlick lab has used tissue engineering principles to produce complex oral-lining tissues that mimic many features of their counterparts found in the oral cavity. Making these tissues was a two-step process. With a combination of chemical signals and specialized surfaces on which these cells attach, an hESC cell line (H9) was directed toward two divergent cell populations. The first population comprises the surface layer (epithelial cells) of complex tissues, while the other is found beneath these cells (mesenchymal cells). Following their isolation and characterization, the team incorporated these two distinct cell populations into the two tissue compartments that comprise these tissue types. The populations were then grown at an air-liquid interface to mimic their growth environment in the oral cavity. Within two weeks, tissues developed that shared many features in common with normal tissues that were constructed with mature cells that are the “gold standard” of normal tissue generation in our lab.

For the first time, researchers have established proof of concept that a single, common source of pluripotent hESC could provide the multiple cell types needed to be recombined within different, but interactive, tissue compartments to generate complex, multilayer tissues. In addition to providing oral mucosal tissues for future transplantation, the tissues generated in these studies can now be used to answer questions regarding the stability and safety of hESC-derived cells and tissues by providing information that will predict how they will respond after therapeutic transplantation in the future.

This is a summary of abstract #3021, “Microenvironmental Cues Direct 3D Tissues from Human Embryonic Stem Cells”, by J. Garlick et al. of Tufts University (Boston, Mass., USA), which was presented at 11:45 a.m. on Saturday, April 4, 2009, in Room D235 of the Miami Beach Convention Center, during the 87th General Session of the International Association for Dental Research.

Popularity: 7% [?]