The secretome obtained from stem cell cultures contains an array of neurotrophic factors and cytokines that might have the potential to treat neurodegenerative conditions. Alzheimer's disease (AD) is one of the most common human late onset and sporadic neurodegenerative disorders. Here, we investigated the therapeutic potential of secretome derived from dental pulp stem cells (DPSCs) to reduce cytotoxicity and apoptosis caused by amyloid beta (Aβ) peptide. We determined whether DPSCs can secrete the Aβ-degrading enzyme, neprilysin (NEP), and evaluated the effects of NEP expression in vitro by quantitating Aβ-degrading activity. The results showed that DPSC secretome contains higher concentrations of VEGF, Fractalkine, RANTES, MCP-1, and GM-CSF compared to those of bone marrow and adipose stem cells. Moreover, treatment with DPSC secretome significantly decreased the cytotoxicity of Aβ peptide by increasing cell viability compared to nontreated cells. In addition, DPSC secretome stimulated the endogenous survival factor Bcl-2 and decreased the apoptotic regulator Bax. Furthermore, neprilysin enzyme was detected in DPSC secretome and succeeded in degrading Aβ 1–42 in vitro in 12 hours. In conclusion, our study demonstrates that DPSCs may serve as a promising source for secretome-based treatment of Alzheimer's disease.

Recent studies have demonstrated that culture under hypoxia has beneficial effects on mesenchymal stem cells (MSCs). However, there are limitations to achieving a stable condition in conventional hypoxic CO2 incubators. DPSCs are a unique type of MSCs which are promising in many regenerative therapies. In this study, we investigated the ideal hypoxic culture environment for DPSCs using a new system that can provide controlled O2 environment. The effects of hypoxia (3%, 5%) on the stemness properties of DPSCs. Their morphology, proliferation rate, expression of stem cell markers, migration ability, mRNA expression of angiogenic/neurotrophic factors and immunomodulatory genes were evaluated and compared. Additionally, the effect of the discrete secretome on proliferation, migration, and neurogenic induction was assessed. Hypoxic DPSCs were found to be smaller in size and exhibited larger nuclei. 5% O2 significantly increased the proliferation rate, migration ability, expression of stem cell markers (CXCR4 and G-CSFR), and expression of SOX2, VEGF, NGF, and BDNF genes of DPSCs. Moreover, secretome collected from 5%O2 cultures displayed higher stimulatory effects on proliferation and migration of NIH3T3 cells and on neuronal differentiation of SH-SY5Y cells. These results demonstrate that 5%O2 may be ideal for enhancing DPSCs growth, stem cell properties, and secretome trophic effect.

The mechanical induction of cell differentiation is well known. However, the effect of mechanical compression on odontoblastic differentiation remains to be elucidated. Thus, we first determined the optimal conditions for the induction of human dental pulp stem cells (hDPSCs) into odontoblastic differentiation in response to mechanical compression of three-dimensional (3D) scaffolds with dentinal tubule-like pores. The odontoblastic differentiation was evaluated by gene expression and confocal laser microscopy. The optimal conditions, which were: cell density, 4.0 × 10 cells/cm ; compression magnitude, 19.6 kPa; and loading time, 9 h, significantly increased expression of the odontoblast-specific markers dentine sialophosphoprotein (DSPP) and enamelysin and enhanced the elongation of cellular processes into the pores of the membrane, a typical morphological feature of odontoblasts. In addition, upregulation of bone morphogenetic protein 7 (BMP7) and wingless-type MMTV integration site family member 10a (Wnt10a) was observed. Moreover, the phosphorylation levels of mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 were also enhanced by mechanical compression, indicating the involvement of the MAPK signalling pathway. It is noteworthy that human mesenchymal stem cells (MSCs) derived from bone marrow and amnion also differentiated into odontoblasts in response to the optimal mechanical compression, demonstrating the importance of the physical structure of the scaffold in odontoblastic differentiation. Thus, odontoblastic differentiation of hDPSCs is promoted by optimal mechanical compression through the MAPK signalling pathway and expression of the BMP7 and Wnt10a genes. The 3D biomimetic scaffolds with dentinal tubule-like pores were critical for the odontoblastic differentiation of MSCs induced by mechanical compression. Copyright © 2014 John Wiley & Sons, Ltd.

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