In the August 16th online edition of Stem Cells, Australian scientists from the University of Queensland (Brisbane), T-L. Chung et al. reported their study results on in vitro epigenetic modification of human embryonic stem cells (hESCs) by the addition of ascorbate to the culture medium. When ascorbated is added to the culture medium there is epigenetic activation of CD30 expression in hESCs. Ascorbate appears to inhibit DNA methylation of the CpG islands within the CD30 promoter region. Analysis of the hESC transcriptome reveals that ascorbate enhances single cell growth as well as inhibiting apoptosis. The authors concluded that their data collectively show that "hESC culture media contain ascorbate trigger CD30 expression through an epigenetic mechanism and that this provides a survival advantage and transcriptome changes that may help adapt hESCs to in vitro culture conditions."

In the June issue of Nature Biotechnology, S. Rodin et al. from the Karolinska Institute (Stockholm, Sweden) reported their study results in long-term propagation of human embryonic stem cells (ESCs) using a human recombinant protein, laminin-511 (α5, β1, γ1 chains) as a substrate, concomitant with defined medium supplemented with human albumin. The hESCS were propagated without feeder cells and the investigators were able to expand and passage (20) the cultures for at least 4 months without a loss in pluripotency. Following long-term cultivation, the scientists were able to differentiate the hESCs into cells all 3 germ layer lineages) as well as maintain the capacity to form teratomas. The researchers also reported that plating clumps of the hESCs onto laminin-511 allowed the cells to adhere to the substrate and form a monolayer culture while maintaining homogeneity in which the experimental results showed 97% of the cells were Oct4+. Adhesion to the substrate was dependent upon the hECC binding α6&beta1 integrin. The author noted that their recombinant substrate provides a novel approach for the generating a homogenous monolayer of hESCs or iPSCs cell cultures, which "provides more controllable conditions" for differentiating pluripotent stem cells down specific cell lineages for future therapeutic purposes.

In the May 27th online edition of PNAS, Japanese scientists, Y. Seiki et al., from the National Institute of Advanced Industrial Science and Technology (Tsukuba) reported the results of their study on the molecular mechanisms for self-renewal, maintenance of pluripotency, and lineage specification in mouse embryonic stem cells (ESCs). The experimental results revealed that a phosphorylation-dependent chromatin relaxation factor, transcriptional intermediary factor-1β (TIF1β), regulates pluripotency in ESCs. Specifically, TIF1β is phosphorylated (at the C-terminal serine 824) and forms a complex with Oct3/4 and chromatin remodeling complex esBAF (Smarcad1, Brg-1, and BAF155) which prolongs the undifferentiated state of ESCs. Remodeling the ESC's chromatin via colocalization of the complexes provides for induction of ESC-specific genes which maintains the ESC's pluripotent state. The investigators also found that TIF1β regulates the reprogramming of somatic cells in a phosphorylation-dependent manner. Ther authors concluded from their study results that "TIF1β provides a phosphorylation-dependent, bidirectional platform for specific transcriptional factors and chromatin remodeling enzymes that regulate the cell differentiation process in the pluripotency of stem cells."

In the May 2nd online edition of Nature Chemical Biology, O. Yanes et al. from The Scripps Research Institute reported their findings on how metabolites modulate differentiation in mouse embryonic stem cells (ESCs). With liquid chromatography-mass spectrometry (LCMS), the investigators analyzed the metabolome of the ESCs using an open-access bioinformatics XCMS platform for data analysis. The experimental results revealed 60 previously unidentified metabolites with highly unsaturated structures whose levels decreased upon differentiation. With oxidized glutathione ratio and ascorbic acid levels as benchmarks, the researchers found that the redox potential in ESCs are regulated during differentiation. By manipulating specific pathways, the study results showed that inhibition of the eicosanoid signaling pathway promoted pluripotency and maintained levels of unsaturated fatty acids in the ESCs. Additionally, downstream oxidation of certain metabolites (e.g. neuroprotetin D1 and acyl-carnitines) promoted neuronal and cardiac differentiation. The authors concluded that their observations suggest that "highly unsaturated metabolome sustained by stem cells allows them to differentiate in response to in vivo oxidative processes such as inflammation."

In the February 22nd online edition of Stem Cells, S. Varhese et al. from Johns Hopkins University published the results of their study on generating human mesenchymal stem cells (hMSCs) from human embryonic germ cells (hEGCs) both in vitro and in vivo. From embryoid bodies, the investigators differentiated hEGCs into mesodermal germ layer lineage expressing markers characteristic of hMSCs and subsequently differntiating into cartilage, bone, and fat. It also noted that after 63 population-doublings, the hEGC-derived cells were able to form hyaline cartilage in vivo without teratoma formation. The authors concluded that the co-culture system "provides new insights into how microenvironmet comprising of extracellular and cellular components may be harnessed to generate hierarchically complex tissues from pluripotent cells."

In the February 22nd issue of the Journal of Cell Biology, T.G. Fazzio and B. Panning reported that certain chromatin regulatory proteins may have an unique function in embryonic stem cells (ESCs). With RNAi screening assays, the investigators found that two genes, Smc2 and Smc4, are essential for proliferation and viability in mouse ESCs. These two genes expressed proteins which are the ccore components of two mammalian condesin complexes. Knockdown experiments (suppressing gene expression of Smc2 & -4) proved to be lethal for ESCs and appeared to have a minimal effect on somatic cells. The investigators reported that inhibiting expression of Smc2 and -4 in ESCs resulted in the cells accumulated massive amount of DNA damage, becoming arrested in metaphase and the nuclei became enlarged and misshapen during interphase. The authors concluded from their experimental results that these condensin complexes regulated interphase chromatin compaction in ESCs. (Since both ESCs and cancer stem cells can self-renew, the authors speculated that it may be possible to develop anti-cancer drugs that can target these condensins.)

In the February 2nd issue of PNAS, R. Gonzalez et al. from The Scripps Research Institute reported their study results on analyzing the extracellular proteome for potential regulators of self renewal in human embryonic stem cells (hESCs). The investigators developed a high-throughput cell-based screening platform to assay for 806 purified secreted proteins that might regulate self renewal in hESCs. The experimental data revealed that a pigment epithelium-derived factor was able to promote long-term growth of hESCs without supplementing the culture media with bFGF or TGFβ/Activin/Nodal ligand. Additionally, the researchers also found that activation of the Erk1/2 signaling pathway by binding the factor to its surface receptor was sufficient to maintain self-renewal and pluripotecy of the hESCs.

In the February issue of FASEB, S. Bonde et al. reported their experimental results on cell fusion with bone marrow cells following transplantation in mice. With a Cre/loxP assay, the investigators found fused cells in the recipient with a myeloid marker (Gr-1+) following a bone marrow transplant. It was also found that fused cells were in high numbers in kidney, Peyer's patch and cardiac tissue. The researchers also conducted experiments demonstrating bone marrow cells fusing with embryonic stem cells. Fusion with embryonic stem cells resulted in reprogrammed tetraploid pluripotent stem cells that were further differentiated into beating cardiomyocytes. The authors concluded from their experimental results that "cell fusion is ubiquitous after cellular transplants and that subsequent sharing of genetic material between the fusion partners affects cellular survival and function."

In the January 17th online edition of Nature Biotechnology, D. James et al. from Weill Cornell Medical College reported their study results on expanding and maintaining endolelial cells which were derived from human embryonic stem cells (hESCs) in vitro. The investigators developed an assay in which a VE-cadherin promoter and a green flourescent protein reporter gene (hVPr-GFP) were used to screen for factors promoting vascular commitment. If an inhibitor to the tranaforming growth factor (TGF)β was introduced into the cultures at day 7 the number of hVPR-GFP+ cells increased by tenfold. Continued inhibition of TGF-β resulted in a 36-fold increase in Id1high, VEGR2high, VE-cadherin+, and ephrinB2+ cells. The experimental results showed that TGF-β inhibition sustains Id1 expression and that Id1 is required for increased proliferation and commitment of the hESCs to the endolthelial lineage. The authors concluded from their study results that "a serum-free method for differentiation and long-term maintenance of hESC-derived endothelial cells" can be used for large scale clinical application.

An interesting paper published in today's (Dec. 21st) online edition of Stem Cells, P. Löser et al. from the Robert Koch Institute (Berlin) reported their retrospective study on the number of human embryonic stem cell (hESCs) lines being used by the international research community. The study presented data from 1,000 research papers published by the end of 2008 on experimental work conducted on hESCs. The authors noted that researchers from the United States had published a predominant number of papers on hESC research. Particularly noteworthy, of the 1,071 original hESC lines derived at 87 institutions in 24 countries, only a fraction of the cell lines were thoroughly characterized. As result of the pleothora of research currently being conducted on induced pluripotent stem (iPS) cells as an alternative to using hESC lines, the authors concluded that a comparison between the use of hESC and iPS cell "application did not show a diminished role for hESC research, but rather revealed until now, both fields further expand, exist independently and partially overlap."