BackgroundIn 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 transient in vitro exposure of MSC to hypoxia, permanent culture under hypoxia should reflect the better physiological conditions.ResultsMorphologic 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".ConclusionThe 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 the in vivo gene signature of MSC, with potential implications in regenerative medicine.

Since the 1960s and the therapeutic use of hematopoietic stem cells of bone marrow origin, there has been an increasing interest in the study of undifferentiated progenitors that have the ability to proliferate and differentiate into various tissues. Stem cells (SC) with different potency can be isolated and characterised. Despite the promise of embryonic stem cells, in many cases, adult or even fetal stem cells provide a more interesting approach for clinical applications. It is undeniable that mesenchymal stem cells (MSC) from bone marrow, adipose tissue, or Wharton's Jelly are of potential interest for clinical applications in regenerative medicine because they are easily available without ethical problems for their uses. During the last 10 years, these multipotent cells have generated considerable interest and have particularly been shown to escape to allogeneic immune response and be capable of immunomodulatory activity. These properties may be of a great interest for regenerative medicine. Different clinical applications are under study (cardiac insufficiency, atherosclerosis, stroke, bone and cartilage deterioration, diabetes, urology, liver, ophthalmology, and organ's reconstruction). This review focuses mainly on tissue and organ regeneration using SC and in particular MSC.

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 at 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.