Background: In the bone marrow, hematopietic and mesenchymal stem cells form a unique niche in which the oxygen tension is low. Hypoxia may have a role in maintaining stem cell fate, self renewal and multipotency. However, whereas most studies addressed the effect of transientin vitroexposure of MSC to hypoxia, permanent culture under hypoxia should reflect the better physiological conditions.Results: Morphologic studies, differentiation and transcriptional profiling experiments were performed on MSC cultured in normoxia (21% O₂) versus hypoxia (5% O₂) for up to passage 2. Cells at passage 0 and at passage 2 were compared, and those at passage 0 in hypoxia generated fewer and smaller colonies than in normoxia. In parallel, MSC displayed (>4 fold) inhibition of genes involved in DNA metabolism, cell cycle progression and chromosome cohesion whereas transcripts involved in adhesion and metabolism (CD93, ESAM, VWF, PLVAP, ANGPT2, LEP, TCF1) were stimulated. Compared to normoxic cells, hypoxic cells were morphologically undifferentiated and contained less mitochondrias. After this lag phase, cells at passage 2 in hypoxia outgrew the cells cultured in normoxia and displayed an enhanced expression of genes (4-60 fold) involved in extracellular matrix assembly (SMOC2), neural and muscle development (NOG, GPR56, SNTG2, LAMA) and epithelial development (DMKN). This group described herein for the first time was assigned by the Gene Ontology program to "plasticity".Conclusion: The duration of hypoxemia is a critical parameter in the differentiation capacity of MSC. Even in growth promoting conditions, hypoxia enhanced a genetic program that maintained the cells undifferentiated and multipotent. This condition may better reflect thein vivogene signature of MSC, with potential implications in regenerative medicine.

The present study was aimed at investigating whether human Periodontal Ligament Stem Cells (hPDLSCs) were capable of sensing and reacting to lipopolysaccharide from Porphyromonas gingivalis (LPS-G) which is widely recognized as a major pathogen in the development and progression of periodontitis. At this purpose hPDLCs were stimulated with 5 μg/mL LPS-G various times and the expression of toll-like receptor 4 (TLR4) was evaluated. Toll-like receptors (TLRs) play an essential role in innate immune signaling in response to microbial infections, and in particular TLR4, type-I transmembrane proteins, has been shown recognizing LPS-G. Our results put in evidence, in treated samples, an overexpression of TLR4 indicating that, hPDLSCs express a functional TLR4 receptor. In addition, LPS-G challenge induces a significant cell growth decrease starting from 24 h until 72 h of treatment. LPS-G leads the activation of the TLR4/MyD88 complex, triggering the secretion of proinflammatory cytokines cascade as: IL-1α, IL-8, TNF-α and β and EOTAXIN. Moreover, the upregulation of pERK/ERK signaling pathways and NFkB nuclear translocation was evident. On the basis of these observations, we conclude that hPDLSCs could represent an appropriate stem cells niche modeling leading to understand and evaluate the biological mechanisms of periodontal stem cells in response to LPS-G, mimicking in vitro an inflammatory process occurring in vivo in periodontal disease.

Objective: The objective of this study was to evaluate the effect of laser irradiation on dog bone marrow stem cells. Background data: Low doses of low-level red laser positively affect the viability of mesenchymal stem cells, and also increase proliferation. Methods: Low-level laser (wavelength, 660 nm; power output, 50 mW), was applied to dog bone marrow stem cell cultures (DBMSC). The energy densities delivered varied from 1 to 12J/cm ² . The effect of the laser irradiation was evaluated on cell proliferation measured with the MTT colorimetric test, cell cycle phase, and on lipidic peroxidation (free radical production). Results: The results indicate that laser irradiation to DBMSC did not change the morphology of the cells, but significantly increased their viability and the number of cells at the G2/M phase with 6, 10, and 12 J/cm ² . On the other hand, malonaldehyde production was significantly enhanced with 8 J/cm ² . Conclusions: The parameters used to irradiate DBMSC increased significantly proliferation without producing high levels of reactive oxygen species (ROS).

With their proliferation, differentiation into specific cell types, and secretion properties, mesenchymal stromal/stem cells (MSC) are very interesting tools to be used in regenerative medicine. Bone marrow (BM) was the first MSC source characterized. In the frame of autologous MSC therapy, it is important to detect donor’s parameters affecting MSC potency. Age of the donors appears as one parameter that could greatly affect MSC properties. Moreover, in vitro cell expansion is needed to obtain the number of cells necessary for clinical developments. It will lead to in vitro cell aging that could modify cell properties. This review recapitulates several studies evaluating the effect of in vitro and in vivo MSC aging on cell properties.