STEM CELLS, a peer reviewed journal published monthly, provides a forum for prompt publication of original investigative papers and concise reviews. STEM CELLS is read and written by clinical and basic scientists whose expertise encompasses the rapidly expanding fields of stem and progenitor cell biology. STEM CELLS welcomes original articles and concise reviews describing basic laboratory investigations of stem cells and the translation of their clinical aspects of characterization and manipulation from the bench to patient care. The journal covers all aspects of stem cells embryonic stem cells/induced pluripotent stem cells; tissue-specific stem cells; stem cell technology: epigenetics, genomics, proteomics, and metabonomics; cancer stem cells; translational and clinical research; and regenerative medicine.

For the accurate determination of gene expression changes during growth and differentiation studies on adipose-derived stem cells (ASCs), quantitative real-time RT-PCR has become a method of choice. The technology is very sensitive, however, without a proper selection of reference genes, to which the genes of interest are normalized, erroneous results may be obtained.

Plasminogen activator inhibitor–1 (PAI-1) plays a key role in control of coagulation and tissue remodeling and has been shown to be regulated by a number of cell stimuli, among those hypoxia. In this study we characterize the hypoxia-mediated induction of PAI-1 in human hepatoma cell line HepG2. We found that PAI-1 is tightly regulated in a narrow oxygen gradient. After incubation at oxygen concentrations of 1% to 2%, a 60-fold increase in PAI-1 messenger RNA levels was observed, whereas mild hypoxic conditions of more than 3.5% did not appear to induce transcription. Moreover, increased levels of PAI-1 protein were observed after incubation at low oxygen tensions. Through sequence analysis, several putative hypoxia-response elements (HREs 1-5) were identified in the human PAI-I promoter. Reporter gene assays showed that the HRE-2 (−194 to −187) was necessary and sufficient for the hypoxia-mediated response. By electrophoretic mobility assay we observed hypoxia-dependent binding of a protein complex to the HRE-2 motif. Further analysis demonstrated that HRE-2 was specifically recognized by the hypoxia-inducible transcription factor 1α–arylhydrocarbon nuclear translocator complex. Taken together, our data demonstrate that hypoxia-induced transcription is mediated through HIF-1 interaction with the HRE-2 site of the human PAI-1 promoter.

Studies of mesenchymal stromal cells (MSC) from BM and adipose tissue have demonstrated similar differentiation potentials along the adipo-, osteo- and chondrogenic lineages. While most clinical trials have been performed using BM-derived MSC, the focus is shifting toward the use of stem cells derived from fat tissue. The aim of the current investigation was to define optimal culture conditions that would facilitate clinical use of adipose-derived stem cells (ASC). Different types and concentrations of serum replacers and basal media were tested with respect to the optimal expansion and subsequent differentiation of primary human ASC. The effect of initial seeding density on the growth of ASC was also determined. While several of the serum replacements proved to be clearly inferior to fetal calf serum (FCS) in promoting ASC growth, the knockout serum replacement (KOSR) had expansion properties similar to those of FCS. However, with respect to the capacity to support adipo-, osteo- and chondrogenic differentiation, KOSR proved to be less consistent than FCS. Among the media formulations, modified Eagle medium alpha supported a significantly faster cell expansion than the other basal media while still maintaining the full differentiation potential of ASC. Regarding the plating density most favorable for rapid expansion, we found that initial plating densities ranging from 100 to 200 cell/cm² resulted in significantly shorter doubling times than plating densities both below and above that range. Identification of the optimal basal medium and serum replacer, together with the most favorable plating density, will facilitate cell-based and tissue-engineering applications employing ASC in pre-clinical and clinical settings.