Embryonic stem cells: staying plastic on plastic

Isolation of Human Oral Keratinocyte Progenitor/Stem Cells

Progenitor/stem cell populations of epithelium are known to reside in the small-sized cell population. Our objective was to physically isolate and characterize an oral keratinocyte-enriched population of small-sized progenitor/stem cells. Primary human oral mucosal keratinocytes cultured in a chemically defined serum-free culture system, devoid of animal-derived feeder cells, were sorted by relative cell size and characterized by immunolabeling for β1 integrin, nuclear transcription factor, peroxisome proliferator-activated receptor-gamma, and cell-cycle analysis. Sorted cells were distinguished as progenitor/stem cells by functional assays and their ability to regenerate an oral mucosal graft. Small-sized cells demonstrated the lowest expression of peroxisome proliferator-activated receptor-gamma, the highest colony-forming efficiency, a longer long-term proliferative potential, an enriched quiescent cell population, and the ability to regenerate an oral mucosal graft, implying that the small-sized cultured oral keratinocytes contained an enriched population of progenitor/stem cells.

Human RGM249-derived small RNAs potentially regulate tumor malignancy

The human noncoding RNA gene RGM249 has been shown to regulate the degree of cancer cell differentiation. In this study, we investigated the effects of 3 microRNA-like molecules digested from RGM249 on the loss of malignant properties in cancer cells in immunodeficient KSN/Slc mice. We utilized small interfering RNAs (siRNAs) alone or in combination with a cationized drug delivery system (DDS) consisting of atelocollagen or gelatin hydrogel microspheres. The results demonstrated growth inhibition and apoptosis and the inhibition of both neovascularization and metastasis, indicating that the DDSs effectively infiltrated the majority of tumor cells in vivo. Systemic administration of the 3 siRNAs inhibited the metastatic ability of malignant cells. Cotransfection of these siRNAs exerted a regulatory effect upon the genes involved in differentiation, pluripotency, and proliferation in cancer cells. These results suggest that RGM249-derived oligonucleotides may be involved in the regulation of metastasis, proliferation, and differentiation in vivo, and that the tested siRNAs may therefore represent a new anticancer therapeutic approach.

The comparison between conditioned media and serum-free media in human embryonic stem cell culture and differentiation

Human embryonic stem cells (hESCs) offer an inexhaustible supply of human somatic cell types through their ability to self-renew while retaining pluripotency. As such, hESC-derived cell types are important for applications ranging from in vitro modeling to therapeutic use. However, for their full potential to be realized, both the growth of the undifferentiated cells and their derivatives must be performed in defined culture conditions. Many research groups maintain hESCs using mouse embryonic fibroblasts (MEF) and MEF conditioned medium (CM). The use of murine systems to support hESCs has been imperative in developing hESC technology; however, they suffer from some major limitations including lack of definition, xenobiotic nature, batch-to-batch variation, and labor-intensive production. Therefore, hESC culture definition is essential if hESC lines, and their derivatives are to be quality assured and manufactured to GMP. We have initiated the process of standardizing hESC tissue culture and have employed two serum-free media: mTeSR (MT) and Stem Pro (SP). hESCs were maintained in a pluripotent state, for over 30 passages using MT and SP. Additionally, we present evidence that hESCs maintained in MT and SP generate equivalent levels of human hepatic endoderm as observed with CM. This data suggests that MT and SP are effective replacements for MEF-CM in hESC culture, contributing to the standardization of hESC in vitro models and ultimately their application.

Pharmacological retention of oral mucosa progenitor/stem cells

Oral mucosa progenitor/stem cells reside as a small-sized cell population that eventually differentiates concurrently with an increase in cell size. Activation of the mammalian target of rapamycin (mTOR) leads to an increase in cell size. We hypothesized that rapamycin, a specific inhibitor of mTOR, will maintain primary human oral keratinocytes as a small-sized, undifferentiated cell population capable of retaining their proliferative capacity. Primary, rapamycin-treated (2 nM, 20 nM) oral keratinocytes showed a diminished cell size that correlated with a higher clonogenicity, a longer-term proliferative potential, and a slower cycling cell population concurrent with decreased expression of a differentiation marker when compared with untreated cells. Only the 2-nM rapamycin-treated oral keratinocytes maintained their ability to regenerate oral mucosa in vitro after 15 weeks of culture. Rapamycin, a Food and Drug Administration-approved drug, may have applicability for use in creating a highly proliferative cell population for use in regenerative medicine.

Nanomedicine for respiratory diseases

Nanotechnology provides new materials in the nanometer range with many potential applications in clinical medicine and research. Due to their unique size-dependent properties nanomaterial such as nanoparticles offer the possibility to develop both new therapeutic and diagnostic tools. Thus, applied nanotechnology to medical problems--nanomedicine--can offer new concepts that are reviewed. The ability to incorporate drugs into nanosystems displays a new paradigm in pharmacotherapy that could be used for cell-targeted drug delivery. Nontargeted nanosystems such as nanocarriers that are coated with polymers or albumin and solid lipid particles have been used as transporter in vivo. However, nowadays drugs can be coupled to nanocarriers that are specific for cells and/or organs. Thus, drugs that are either trapped within the carriers or deposited in subsurface oil layers could be specifically delivered to organs, tumors and cells. These strategies can be used to concentrate drugs in selected target tissues thus minimizing systemic side effects and toxicity. In addition to these therapeutic options, nanoparticle-based "molecular" imaging displays a field in which this new technology has set the stage for an evolutionary leap in diagnostic imaging. Based on the recent progress in nanobiotechnology there is potential for nanoparticles and -systems to become useful tools as therapeutic and diagnostic tools in the near future.

HOXB4-induced self-renewal of hematopoietic stem cells is significantly enhanced by p21 deficiency

Enforced expression of the HOXB4 transcription factor and downregulation of p21(Cip1/Waf) (p21) can each independently increase proliferation of murine hematopoietic stem cells (HSCs). We asked whether the increase in HSC self-renewal generated by overexpression of HOXB4 is enhanced in p21-deficient HSCs. HOXB4 was overexpressed in hematopoietic cells from wild-type (wt) and p21-/- mice. Bone marrow (BM) cells were transduced with a retroviral vector expressing HOXB4 together with GFP (MIGB4), or a control vector containing GFP alone (MIG) and maintained in liquid culture for up to 11 days. At day 11 of the expansion culture, the number of primary CFU-GM (colony-forming unit granulocyte-macrophage) colonies and the repopulating ability were significantly increased in MIGB4 p21-/- BM (p21B4) cells compared with MIGB4-transduced wt BM (wtB4) cells. To test proliferation of HSCs in vivo, we performed competitive repopulation experiments and obtained significantly higher long-term engraftment of expanded p21B4 cells compared with wtB4 cells. The 5-day expansion of p21B4 HSCs generated 100-fold higher numbers of competitive repopulating units compared with wtMIG and threefold higher numbers compared with wtB4. The findings demonstrate that increased expression of HOXB4, in combination with suppression of p21 expression, could be a useful strategy for effective and robust expansion of HSCs.

Human embryonic stem cells express an immunogenic nonhuman sialic acid

Human embryonic stem cells (HESC) can potentially generate every body cell type, making them excellent candidates for cell- and tissue-replacement therapies. HESC are typically cultured with animal-derived 'serum replacements' on mouse feeder layers. Both of these are sources of the nonhuman sialic acid Neu5Gc, against which many humans have circulating antibodies. Both HESC and derived embryoid bodies metabolically incorporate substantial amounts of Neu5Gc under standard conditions. Exposure to human sera with antibodies specific for Neu5Gc resulted in binding of immunoglobulin and deposition of complement, which would lead to cell killing in vivo. Levels of Neu5Gc on HESC and embryoid bodies dropped after culture in heat-inactivated anti-Neu5Gc antibody-negative human serum, reducing binding of antibodies and complement from high-titer sera, while allowing maintenance of the undifferentiated state. Complete elimination of Neu5Gc would be likely to require using human serum with human feeder layers, ideally starting with fresh HESC that have never been exposed to animal products.

Establishment and maintenance of human embryonic stem cell lines on human feeder cells derived from uterine endometrium under serum-free condition

Human embryonic stem (hES) cells are usually established and maintained on mouse embryonic fibroblast (MEFs) feeder layers. However, it is desirable to develop human feeder cells because animal feeder cells are associated with risks such as viral infection and/or pathogen transmission. In this study, we attempted to establish new hES cell lines using human uterine endometrial cells (hUECs) to prevent the risks associated with animal feeder cells and for their eventual application in cell-replacement therapy. Inner cell masses (ICMs) of cultured blastocysts were isolated by immunosurgery and then cultured on mitotically inactivated hUEC feeder layers. Cultured ICMs formed colonies by continuous proliferation and were allowed to proliferate continuously for 40, 50, and 55 passages. The established hES cell lines (Miz-hES-14, -15, and -9, respectively) exhibited typical hES cells characteristics, including continuous growth, expression of specific markers, normal karyotypes, and differentiation capacity. The hUEC feeders have the advantage that they can be used for many passages, whereas MEF feeder cells can only be used as feeder cells for a limited number of passages. The hUECs are available to establish and maintain hES cells, and the high expression of embryotrophic factors and extracellular matrices by hUECs may be important to the efficient growth of hES cells. Clinical applications require the establishment and expansion of hES cells under stable xeno-free culture systems.