No abstract

Angiogenesis, the formation of capillaries from pre-existing blood vessels, is a key process in tissue engineering. If blood supply cannot be established rapidly, there is insufficient oxygen and nutrient transport and necrosis of the implanted tissue will occur. Recent studies indicate that the human dental pulp contains precursor cells, named dental pulp stem cells (hDPSC) that show self-renewal and multilineage differentiation capacity. Since these cells can be easily isolated, cultured and cryopreserved, they represent an attractive stem cell source for tissue engineering. Until now, only little is known about the angiogenic abilities and mechanisms of the hDPSC. In this study, the angiogenic profile of both cell lysates and conditioned medium of hDPSC was determined by means of an antibody array. Numerous pro-and anti-angiogenic factors such as vascular endothelial growth factor (VEGF), monocyte chemotactic protein-1 (MCP-1), plasminogen activator inhibitor-1 (PAI-1) and endostatin were found both at the mRNA and protein level. hDPSC had no influence on the proliferation of the human microvascular endothelial cells (HMEC-1), but were able to significantly induce HMEC-1 migration in vitro. Addition of the PI3K-inhibitor LY294002 and the MEK-inhibitor U0126 to the HMEC-1 inhibited this effect, suggesting that both Akt and ERK pathways are involved in hDPSC-mediated HMEC-1 migration. Antibodies against VEGF also abolished the chemotactic actions of hDPSC. Furthermore, in the chicken chorioallantoic membrane (CAM) assay, hDPSC were able to significantly induce blood vessel formation. In conclusion, hDPSC have the ability to induce angiogenesis, meaning that this stem cell population has a great clinical potential, not only for tissue engineering but also for the treatment of chronic wounds, stroke and myocardial infarctions.

Dental pulp stem cells (DPSCs) are an attractive alternative mesenchymal stem cell (MSC) source because of their isolation simplicity compared with the more invasive methods associated with harvesting other MSC sources. However, the isolation method to be favored for obtaining DPSC cultures remains under discussion. This study compares the stem cell properties and multilineage differentiation potential of DPSCs obtained by the two most widely adapted isolation procedures. DPSCs were isolated either by enzymatic digestion of the pulp tissue (DPSC-EZ) or by the explant method (DPSC-OG), while keeping the culture media constant throughout all experiments and in both isolation methods. Assessment of the stem cell properties of DPSC-EZ and DPSC-OG showed no significant differences between the two groups with regard to proliferation rate and colony formation. Phenotype analysis indicated that DPSC-EZ and DPSC-OG were positive for CD29, CD44, CD90, CD105, CD117 and CD146 expression without any significant differences. The multilineage differentiation potential of both stem cell types was confirmed by using standard immuno(histo/cyto)chemical staining together with an in-depth ultrastructural analysis by means of transmission electron microscopy. Our results indicate that both DPSC-EZ and DPSC-OG could be successfully differentiated into adipogenic, chrondrogenic and osteogenic cell types, although the adipogenic differentiation of both stem cell populations was incomplete. The data suggest that both the enzymatic digestion and outgrowth method can be applied to obtain a suitable autologous DPSC resource for tissue replacement therapies of both bone and cartilage.

In the present study, we evaluated the differentiation potential of human dental pulp stem cells (hDPSCs) toward Schwann cells, together with their functional capacity with regard to myelination and support of neurite outgrowth in vitro. Successful Schwann cell differentiation was confirmed at the morphological and ultrastructural level by transmission electron microscopy. Furthermore, compared to undifferentiated hDPSCs, immunocytochemistry and ELISA tests revealed increased glial marker expression and neurotrophic factor secretion of differentiated hDPSCs (d-hDPSCs), which promoted survival and neurite outgrowth in 2-dimensional dorsal root ganglia cultures. In addition, neurites were myelinated by d-hDPSCs in a 3-dimensional collagen type I hydrogel neural tissue construct. This engineered construct contained aligned columns of d-hDPSCs that supported and guided neurite outgrowth. Taken together, these findings provide the first evidence that hDPSCs are able to undergo Schwann cell differentiation and support neural outgrowth in vitro, proposing them to be good candidates for cell-based therapies as treatment for peripheral nerve injury.—Martens, W., Sanen, K., Georgiou, M., Struys, T., Bronckaers, A., Ameloot, M., Phillips, J., Lambrichts, I. Human dental pulp stem cells can differentiate into Schwann cells and promote and guide neurite outgrowth in an aligned tissue-engineered collagen construct in vitro.

Cell-based therapies are emerging as an alternative treatment option to promote functional recovery in patients suffering from neurological disorders, which are the major cause of death and permanent disability. The present study aimed to differentiate human dental pulp stem cells (hDPSCs) toward functionally active neuronal cells in vitro. hDPSCs were subjected to a two-step protocol. First, neuronal induction was acquired through the formation of neurospheres, followed by neuronal maturation, based on cAMP and neurotrophin-3 (NT-3) signaling. At the ultrastructural level, it was shown that the intra-spheral microenvironment promoted intercellular communication. hDPSCs grew out of the neurospheres in vitro and established a neurogenic differentiated hDPSC culture (d-hDPSCs) upon cAMP and NT-3 signaling. d-hDPSCs were characterized by the increased expression of neuronal markers such as neuronal nuclei, microtubule-associated protein 2, neural cell adhesion molecule, growth-associated protein 43, synapsin I, and synaptophysin compared with nondifferentiated hDPSCs. Enzyme-linked immunosorbent assay demonstrated that the secretion of brain-derived neurotrophic factor, vascular endothelial growth factor, and nerve growth factor differed between d-hDPSCs and hDPSCs. d-hDPSCs acquired neuronal features, including multiple intercommunicating cytoplasmic extensions and increased vesicular transport, as shown by the electron microscopic observation. Patch clamp analysis demonstrated the functional activity of d-hDPSCs by the presence of tetrodotoxin- and tetraethyl ammonium-sensitive voltage-gated sodium and potassium channels, respectively. A subset of d-hDPSCs was able to fire a single action potential. The results reported in this study demonstrate that hDPSCs are capable of neuronal commitment following neurosphere formation, characterized by distinct morphological and electrophysiological properties of functional neuronal cells.

Within the field of dental tissue engineering, the establishment of adequate tissue vascularization is one of the most important burdens to overcome. As vascular access within the tooth is restricted by the apical foramen, it is of major importance to implement effective vascularization strategies in order to recreate viable components of teeth and periodontal tissues. However, while the current regenerative approaches focus on the use of dental stem cells (DSCs), little is known about these cells and their ability to promote angiogenesis. Therefore, the present study aimed to elucidate the paracrine angiogenic properties of postnatal DSCs, in particular dental pulp stem cells (DPSCs), stem cells from the apical papilla (SCAPs) and dental follicle precursor cells (FSCs). An antibody array, together with RT-PCR and ELISA, pointed out the differential expression of pro-angiogenic as well as anti-angiogenic factors by cultured DSCs and human gingival fibroblasts (HGF-1). Despite the secretion of proliferation-promoting factors, DSCs caused no notable increase in the proliferation of human microvascular endothelial cells (HMEC-1). With regard to other aspects of the angiogenic cascade, DPSCs, SCAPs and HGF-1 significantly promoted endothelial migration in a transwell migration assay. DPSCs also had a pronounced effect on endothelial tubulogenesis, as was shown by an in vitro Matrigel™ assay. In the last part of this study, a chorioallantoic membrane assay demonstrated a sustained pro-angiogenic impact of DPSCs and SCAPs in an in vivo setting. Collectively, these data indicate a predominant pro-angiogenic influence of DPSCs and SCAPS in vitro and in vivo in comparison to FSCs, suggesting that both stem cell populations could potentially promote the vascularization of regenerated dental tissues.

No abstract

SummaryTools for rapid and efficient transgenesis in “safe harbor” loci in an isogenic context remain important to exploit the possibilities of human pluripotent stem cells (hPSCs). We created hPSC master cell lines suitable for FLPe recombinase-mediated cassette exchange (RMCE) in the AAVS1 locus that allow generation of transgenic lines within 15 days with 100% efficiency and without random integrations. Using RMCE, we successfully incorporated several transgenes useful for lineage identification, cell toxicity studies, and gene overexpression to study the hepatocyte lineage. However, we observed unexpected and variable transgene expression inhibition in vitro, due to DNA methylation and other unknown mechanisms, both in undifferentiated hESC and differentiating hepatocytes. Therefore, the AAVS1 locus cannot be considered a universally safe harbor locus for reliable transgene expression in vitro, and using it for transgenesis in hPSC will require careful assessment of the function of individual transgenes.