Angiogenic Potential and Secretome of Human Apical Papilla Mesenchymal Stem Cells in Various Stress Microenvironments

Angiogenic Potential of Various Oral Cavity-Derived Mesenchymal Stem Cells and Cell-Derived Secretome: A Systematic Review and Meta-Analysis

Recent evidence suggests the immense potential of human mesenchymal stem cell (hMSC) secretome conditioned medium-mediated augmentation of angiogenesis. However, angiogenesis potential varies from source and origin. The hMSCs derived from the oral cavity share an exceptional quality due to their origin from a hypoxic environment. Our systematic review aimed to compare the mesenchymal stem cells (MSCs) derived from various oral cavity sources and cell-derived secretomes, and evaluate their angiogenic potential. A literature search was conducted using PubMed and Scopus from January 2000 to September 2020. Source-wise outcomes were systematically analyzed using in vitro, in vivo, and in ovo studies, emphasizing endothelial cell migration, tube formation, and blood vessel formation. Ninety-four studies were included in the systematic review, out of which 4 studies were subsequently included in the meta-analysis. Prominent growth factors and other bioactive components implicated in improving angiogenesis were included in the respective studies. The findings suggest that oral tissues are a rich source of hMSCs. The meta-analysis revealed a positive correlation between dental pulp-derived MSCs (DPMSCs) and stem cells derived from apical papilla (SCAP) compared to human umbilical cord-derived endothelial cell lines as a control. It shows a statistically significant positive correlation between the co-culture of human umbilical vein endothelial cells (HUVECs) and DPMSCs with tubule length formation and total branching points. Our meta-analysis revealed that oral-derived MSCs (dental pulp stem cells and SCAP) carry a better angiogenic potential in vitro than endothelial cell lines alone. The reviewed literature illustrates that oral cavity-derived MSCs (OC-MSCs) increased angiogenesis. The present literature reveals a dearth of investigations involving sources other than dental pulp. Even though OC-MSCs have revealed more significant potential than other MSCs, more comprehensive, target-oriented interinstitutional prospective studies are warranted to determine whether oral cavity-derived stem cells are the most excellent sources of significant angiogenic potential.

The Effects of Hypoxia-Preconditioned Dental Stem Cell-Derived Secretome on Tissue Regeneration

Mesenchymal stroma cells derived from oral tissues are known as dental stem cells (DSCs). Owing to their unique therapeutic niche and clinical accessibility, DSCs serve as a promising treatment option for bone defects and oral tissue regeneration. DSCs exist in a hypoxic microenvironment in vivo, which is far lower than the current 20% oxygen concentration used in in vitro culture. It has been widely reported that the application of an oxygen concentration less than 5% in the culture of DSCs is beneficial for preserving stemness and promoting proliferation, migration, and paracrine activity. The paracrine function of DSCs involves the secretome, which includes conditioned media (CM) and soluble bioactive molecules, as well as extracellular vesicles extracted from CM. Hypoxia can play a role in immunomodulation and angiogenesis by altering the protein or nucleic acid components in the secretory group, which enhances the therapeutic potential of DSCs. This review summarizes the biological characteristics of DSCs, the influence of hypoxia on DSCs, the impact of hypoxia on the secretory group of DSCs, and the latest progress on the use of DSCs secretory group in tissue regeneration based on hypoxia pretreatment. We highlighted the multifunctional biological effect of hypoxia culture on tissue regeneration and provided a summary of the current mechanism of hypoxia in the pretreatment of DSCs.

Apical papilla stem cell-derived exosomes regulate lipid metabolism and alleviate inflammation in the MCD-induced mouse NASH model

Stem cells from the apical papilla(SCAPs) exhibit remarkable tissue repair capabilities, demonstrate anti-inflammatory and pro-angiogenic effects, positioning them as promising assets in the realm of regenerative medicine. Recently, the focus has shifted towards exosomes derived from stem cells, perceived as safer alternatives while retaining comparable physiological functions. This study delves into the therapeutic implications of exosomes derived from SCAPs in the methionine-choline-deficient (MCD) diet-induced mice non-alcoholic steatohepatitis (NASH) model. We extracted exosomes from SCAPs. During the last two weeks of the MCD diet, mice were intravenously administered SCAPs-derived exosomes at two distinct concentrations (50 μg/mouse and 100 μg/mouse) biweekly. Thorough examinations of physiological and biochemical indicators were performed to meticulously evaluate the impact of exosomes derived from SCAPs on the advancement of NASH in mice induced by MCD diet. This findings revealed significant reductions in body weight loss and liver damage induced by the MCD diet following exosomes treatment. Moreover, hepatic fat accumulation was notably alleviated. Mechanistically, the treatment with exosomes led to an upregulation of phosphorylated adenosine monophosphate-activated protein kinase (p-AMPK) levels in the liver, enhancing hepatic fatty acid oxidation and transporter gene expression while inhibiting genes associated with fatty acid synthesis. Additionally, exosomes treatment increased the transcription levels of key liver mitochondrial marker proteins and the essential mitochondrial biogenesis factor. Furthermore, the levels of serum inflammatory factors and hepatic tissue inflammatory factor mRNA expression were significantly reduced, likely due to the anti-inflammatory phenotype induced by exosomes in macrophages. The above conclusion suggests that SCAPs-exosomes can improve NASH.

ADAMTS13 regulates angiogenic markers via Ephrin/Eph signaling in human mesenchymal stem cells under serum-deprivation stress

Mesenchymal stem cells (MSCs) are known to facilitate angiogenesis and promote neo-vascularization via secretion of trophic factors. Here, we explored the molecular mechanism adopted by ADAMTS13 in modulating the expression of some key angiogenic markers in human umbilical cord-derived MSCs under serum-deprivation stress. Wharton's jelly MSCs (WJ-MSCs) were isolated from the perivascular region of human umbilical cords by explant culture. ADAMTS13 was upregulated at both mRNA and protein levels in WJ-MSCs under serum-deprivation stress. Correspondingly, some key angiogenic markers were also seen to be upregulated. By screening signaling pathways, p38 and JNK pathways were identified as negative and positive regulators for expression of ADAMTS13, and the angiogenic markers, respectively. Our results also indicated the Notch pathway and p53 as other probable partners modulating the expression of ADAMTS13 and the angiogenic markers. Knockdown of ADAMTS13 using siRNA led to reversal in the expression of these angiogenic markers. Further, ADAMTS13 was shown to act via the EphrinB2/EphB4 axis followed by ERK signaling to control expression of the angiogenic markers. Interestingly, stronger expression levels were noted for ADAMTS13, VEGF and PDGF under a more stringent nutrient stress condition. Thus, we highlight a novel role of ADAMTS13 in WJ-MSCs under nutrient stress condition.

Exosomes derived from stem cells from apical papilla promote angiogenesis via miR-126 under hypoxia

OBJECTIVES

To explore the effect of exosomal miR-126 derived from stem cells from the apical papilla (SCAPs) under hypoxia on human umbilical vein endothelial cell (HUVEC) angiogenesis.

METHODS

miR-126 mimics plasmids were used to upregulate miR-126 in SCAPs. Internalization of PKH26-labeled exosomes was examined by fluorescent microscopy. CCK-8 assay, Transwell assay, scratch assay, tube formation assay, and Matrigel plug assay were performed to detect the effects of exosomes on the angiogenic ability of HUVECs. The luciferase reporter assay and rescue assay were performed to examine the relationship between miR-126 and sprouty-related, EVH1 domain-containing protein 1 (SPRED1). The involvement of SPRED1 and the extracellular signal-regulated kinase (ERK) signaling pathway was evaluated by western blotting.

RESULTS

miR-126 expression was upregulated in SCAPs and in SCAP-derived exosomes under hypoxia. miR-126 expression was increased in HUVECs when cocultured with SCAP-derived exosomes. Induced overexpression of miR-126 in hypoxic SCAPs and secreted exosomes resulted in enhanced angiogenesis both in vitro and in vivo. Western blot analysis revealed that miR-126-mediated SPRED1 downregulation induced activation of ERK signaling.

CONCLUSIONS

Under hypoxic conditions, exosomes derived from SCAPs can promote HUVEC angiogenesis through expression of miR-126, which subsequently suppresses SPRED1 and activates the ERK signaling pathway.

Serum starvation affects mitochondrial metabolism of adipose-derived stem/stromal cells

BACKGROUND AIMS

A large part of mesenchymal stromal cell (MSC) regenerative and immunomodulatory action is mediated by paracrine signaling. Hence, an increasing body of evidence acknowledges the potential of MSC secretome in a variety of preclinical and clinical scenarios. Mid-term serum deprivation is a common approach in the pipeline of MSC secretome production. Nevertheless, up to now, little is known about the impact of this procedure on the metabolic status of donor cells.

METHODS

Here, through untargeted differential metabolomics, we revealed an impairment of mitochondrial metabolism in adipose-derived MSCs exposed for 72 h to serum deprivation.

RESULTS

This evidence was further confirmed by the significant accumulation of reactive oxygen species and the reduction of succinate dehydrogenase activity. Probably as a repair mechanism, an upregulation of mitochondrial superoxide dismutase was also induced.

CONCLUSIONS

Of note, the analysis of mitochondrial functionality indicated that, despite a significant reduction of basal respiration and ATP production, serum-starved MSCs still responded to changes in energy demand. This metabolic phenotype correlates with the obtained evidence of mitochondrial elongation and branching upon starvation.

Coordinated reprogramming of renal cancer transcriptome, metabolome and secretome associates with immune tumor infiltration

BACKGROUND

Clear cell renal cell carcinoma (ccRCC) is the most common subtype of renal cancer. The molecules (proteins, metabolites) secreted by tumors affect their extracellular milieu to support cancer progression. If secreted in amounts detectable in plasma, these molecules can also serve as useful, minimal invasive biomarkers. The knowledge of ccRCC tumor microenvironment is fragmentary. In particular, the links between ccRCC transcriptome and the composition of extracellular milieu are weakly understood. In this study, we hypothesized that ccRCC transcriptome is reprogrammed to support alterations in tumor microenvironment. Therefore, we comprehensively analyzed ccRCC extracellular proteomes and metabolomes as well as transcriptomes of ccRCC cells to find molecules contributing to renal tumor microenvironment.

METHODS

Proteomic and metabolomics analysis of conditioned media isolated from normal kidney cells as well as five ccRCC cell lines was performed using mass spectrometry, with the following ELISA validation. Transcriptomic analysis was done using microarray analysis and validated using real-time PCR. Independent transcriptomic and proteomic datasets of ccRCC tumors were used for the analysis of gene and protein expression as well as the level of the immune infiltration.

RESULTS

Renal cancer secretome contained 85 proteins detectable in human plasma, consistently altered in all five tested ccRCC cell lines. The top upregulated extracellular proteins included SPARC, STC2, SERPINE1, TGFBI, while downregulated included transferrin and DPP7. The most affected extracellular metabolites were increased 4-hydroxy-proline, succinic acid, cysteine, lactic acid and downregulated glutamine. These changes were associated with altered expression of genes encoding the secreted proteins (SPARC, SERPINE1, STC2, DPP7), membrane transporters (SLC16A4, SLC6A20, ABCA12), and genes involved in protein trafficking and secretion (KIF20A, ANXA3, MIA2, PCSK5, SLC9A3R1, SYTL3, and WNTA7). Analogous expression changes were found in ccRCC tumors. The expression of SPARC predicted the infiltration of ccRCC tumors with endothelial cells. Analysis of the expression of the 85 secretome genes in > 12,000 tumors revealed that SPARC is a PanCancer indicator of cancer-associated fibroblasts' infiltration.

CONCLUSIONS

Transcriptomic reprogramming of ccRCC supports the changes in an extracellular milieu which are associated with immune infiltration. The proteins identified in our study represent valuable cancer biomarkers detectable in plasma.

Effect of Long-Term Cryopreservation on the Stemness of Stem Cells of Apical Papilla

Stem cells of apical papilla (SCAPs) are considered a subpopulation of dental stem cells with unique properties. They originate from a developing tissue, the apical papilla of developing teeth, a characteristic that enhances their stemness. Banking of these stem cells can offer a source of dental stem cells for future regenerative therapies. Until now, only the effect of six months' cryopreservation on SCAPs has been studied. In this study, the long-term (19 months) effect of cryopreservation on SCAPs was examined by means of estimation of their differentiation's capacity, flow cytometry immunophenotypical characterization, and molecular characterization of the main transcriptional factors that coincide with pluripotency. As was indicated from our results, 19-month cryopreservation of SCAPs did not affect negatively their stemness; since no significant difference was observed on their typical fibroblast-like morphology, they retained their differentiation capacity, and no discrepancies were found either on immunophenotypical level or molecular level.

Potential neuroprotective effect of stem cells from apical papilla derived extracellular vesicles enriched by lab-on-chip approach during retinal degeneration

Retinal degeneration (RD) is recognized as a frequent cause of visual impairments, including inherited (Retinitis pigmentosa) and degenerative (age-related macular) eye diseases. Dental stem cells (DSCs) have recently demonstrated a promising neuroprotection potential for ocular diseases through a paracrine manner carried out by extracellular vesicles (EVs). However, effective isolation of EVs is still challenging, and isolation methods determine the composition of enriched EVs and the subsequent biological and functional effects. In the present study, we assessed two enrichment methods (micro-electromechanical systems and ultrafiltration) to isolate the EVs from stem cells from apical papilla (SCAP). The size distribution of the corresponding isolates exhibited the capability of each method to enrich different subsets of EVs, which significantly impacts their biological and functional effects. We confirmed the neuroprotection and anti-inflammatory capacity of the SCAP-EVs in vitro. Further experiments revealed the possible therapeutic effects of subretinal injection of SCAP-EVs in the Royal College of Surgeons (RCS) rat model. We found that EVs enriched by the micro-electromechanical-based device (MEMS-EVs) preserved visual function, reduced retinal cell apoptosis, and prevented thinning of the outer nuclear layer (ONL). Interestingly, the effect of MEMS-EVs was extended to the retinal ganglion cell/retinal nerve fiber layer (GCL/RNFL). This study supports the use of the microfluidics approach to enrich valuable subsets of EVs, together with the choice of SCAP as a source to derive EVs for cell-free therapy of RD.

Novel Antibacterial Properties of the Human Dental Pulp Multipotent Mesenchymal Stromal Cell Secretome

It is well recognized that clearance of bacterial infection within the dental pulp precedes pulpal regeneration. However, although the regenerative potential of the human dental pulp has been investigated extensively, its antimicrobial potential remains to be examined in detail. In the current study bactericidal assays were used to demonstrate that the secretome of dental pulp multipotent mesenchymal stromal cells (MSCs) has direct antibacterial activity against the archetypal Gram-positive and Gram-negative bacteria, Staphylococcus aureus and Escherichia coli, respectively, as well as the oral pathogens Streptococcus mutans, Lactobacillus acidophilus, and Fusobacterium nucleatum. Furthermore, a cytokine/growth factor array, enzyme-linked immunosorbent assays, and antibody blocking were used to show that cytokines and growth factors present in the dental pulp MSC secretome, including hepatocyte growth factor, angiopoietin-1, IL-6, and IL-8, contribute to this novel antibacterial activity. This study elucidated a novel and diverse antimicrobial secretome from human dental pulp MSCs, suggesting that these cells contribute to the antibacterial properties of the dental pulp. With this improved understanding of the secretome of dental pulp MSCs and its novel antibacterial activity, new evidence for the ability of the dental pulp to fight infection and restore functional competence is emerging, providing further support for the biological basis of pulpal repair and regeneration.

Dental stem cell-conditioned medium for tissue regeneration: Optimization of production and storage

BACKGROUND

Mesenchymal stem cells (MSC) effects on tissue regeneration are mainly mediated by their secreted substances (secretome), inducing their paracrine activity. This Conditioned medium (CM), including soluble factors (proteins, nucleic acids, lipids) and extracellular vesicles is emerging as a potential alternative to cell therapy. However, the manufacturing of CM suffers from variable procedures and protocols leading to varying results between studies. Besides, there is no well-defined optimized procedure targeting specific applications in regenerative medicine.

AIM

To focus on conditioned medium produced from dental MSC (DMSC-CM), we reviewed the current parameters and manufacturing protocols, in order to propose a standardization and optimization of these manufacturing procedures.

METHODS

We have selected all publications investigating the effects of dental MSC secretome in in vitro and in vivo models of tissue regeneration, in accordance with the PRISMA guidelines.

RESULTS

A total of 351 results were identified. And based on the inclusion criteria described above, 118 unique articles were included in the systematic review. DMSC-CM production was considered at three stages: before CM recovery (cell sources for CM), during CM production (culture conditions) and after production (CM treatment).

CONCLUSION

No clear consensus could be recovered as evidence-based methods, but we were able to describe the most commonly used protocols: donors under 30 years of age, dental pulp stem cells and exfoliated deciduous tooth stem cells with cell passage between 1 and 5, at a confluence of 70% to 80%. CM were often collected during 48 h, and stored at -80 °C. It is important to point out that the preconditioning environment had a significant impact on DMSC-CM content and efficiency.

Oral stem cells, decoding and mapping the resident cells populations

The teeth and their supporting tissues provide an easily accessible source of oral stem cells. These different stem cell populations have been extensively studied for their properties, such as high plasticity and clonogenicity, expressing stem cell markers and potency for multilineage differentiation in vitro. Such cells with stem cell properties have been derived and characterised from the dental pulp tissue, the apical papilla region of roots in development, as well as the supporting tissue of periodontal ligament that anchors the tooth within the alveolar socket and the soft gingival tissue. Studying the dental pulp stem cell populations in a continuously growing mouse incisor model, as a traceable in vivo model, enables the researchers to study the properties, origin and behaviour of mesenchymal stem cells. On the other side, the oral mucosa with its remarkable scarless wound healing phenotype, offers a model to study a well-coordinated system of healing because of coordinated actions between epithelial, mesenchymal and immune cells populations. Although described as homogeneous cell populations following their in vitro expansion, the increasing application of approaches that allow tracing of individual cells over time, along with single-cell RNA-sequencing, reveal that different oral stem cells are indeed diverse populations and there is a highly organised map of cell populations according to their location in resident tissues, elucidating diverse stem cell niches within the oral tissues. This review covers the current knowledge of diverse oral stem cells, focusing on the new approaches in studying these cells. These approaches "decode" and "map" the resident cells populations of diverse oral tissues and contribute to a better understanding of the "stem cells niche architecture and interactions. Considering the high accessibility and simplicity in obtaining these diverse stem cells, the new findings offer potential in development of translational tissue engineering approaches and innovative therapeutic solutions.

Neural Differentiation of Human Dental Mesenchymal Stem Cells Induced by ATRA and UDP-4: A Comparative Study

Human mesenchymal stem cells (MSC) are multipotent stem cells, which are isolated from various sources. Currently, there is a worldwide interest for dental MSC to be used against neurodegenerative diseases, since they derive from the neural crest and express embryonic stem cell markers. This fact prompted us to explore their potential for neural trans-differentiation in culture. We employed all-trans-retinoic acid (ATRA) and 2-(3-ethylureido)-6-methylpyridine (UDP-4) to induce neural differentiation of human MSC from the dental apical papilla (SCAP). The SCAP were exposed to either agent separately and assessed for proliferation, viability, morphology, and gene expression of the following neural-specific markers: neuron-specific enolase (ENO2), neurofibromin 1 (NF1), choline acetyltransferase (CHAT), tyrosine hydroxylase (TH), and the vesicular GABA transporter (SLC32A1). They were also assessed for the expression of glial fibrillary acidic protein (GFAP) and neuronal nuclear antigen (NeuN) by immunofluorescence. ATRA or UDP-4 treatment inhibited the cell growth and promoted limited cell death, but to a different extent. The addition of the neuroprotective agent recombinant human erythropoietin-alpha (rhEPO-α) enhanced the UDP-4-inducing capacity for more than three weeks. ATRA or UDP-4 treatment significantly upregulated ENO2 and NF1 expression, indicating neuronal differentiation. Moreover, the ATRA treatment significantly induced the upregulation of the GABAergic-specific SLC32A1, while the UDP-4 treatment led to the significant upregulation of the adrenergic-specific TH. The UDP-4 treatment induced the expression of NeuN and GFAP after four and three weeks, respectively, while the ATRA-treatment did not. Our findings indicate that SCAP can be differentiated into neural-like cells after treatment with ATRA or UDP-4 by exhibiting a disparate pattern of differentiation. Therefore, UDP-4 is suggested here as a new potent neural-differentiation-inducing compound, which, when combined with rhEPO-α, could lay the foundation for robust stem-cell-based therapies of neurodegeneration.

Calcium silicate-based cements affect the cell viability and the release of TGF-β1 from apical papilla cells

This study investigated the cytotoxicity and release of Transforming Growth Factor Beta 1 (TGF-β1) from cultured human apical papilla cells (APCs) after application of four bioactive materials. Culture of APCs was established and used for cytotoxic and quantitative assays. Extracts of Biodentine, Bio-C Repair, MTA Repair and White MTA were prepared and diluted (1, 1:4 and 1:16) and used for MTT assays up to 72 h. Total TGF-β1 was quantified by ELISA. Data were analyzed by ANOVA and Tukey's test (α = 0.05). For Biodentine, at 24 h and 48 h, cell viability was lower than control (p < 0.05). At 72 h, only undiluted extract of Biodentine were cytotoxic (p < 0.05). At 24 h, a cytotoxic effect was found for undiluted and 1:4 dilution of Bio-C Repair (p < 0.05). At 48 h, however, Bio-C Repair at 1:4 and 1:8 dilution showed higher cell viability (p < 0.05). At 24 and 48 h, the cell viability for undiluted MTA Repair were higher than control (p < 0.05). For White MTA, at 24 and 48 h, all dilutions were cytotoxic (p < 0.05). All cements led to reduced release of total TGF-β1 from the APCs (p < 0.05). In conclusion, cell viability varied depending on the material and dilution. Only Bio-C repair and MTA repair led to higher cell viability of APCs. All materials induced a decrease in the release of total TGF-β1 from the APCs.

In vitro evaluation of periapical lesion-derived stem cells for dental pulp tissue engineering

Dental pulp tissue engineering is a promising alternative treatment for pulpitis and periapical periodontitis, and dental pulp stem cells (DPSCs) are considered to be the gold standard for dental seed cell research. Periapical lesions harbor mesenchymal stem cells with the capacity for self-renewal and multilineage differentiation. However, it remains unknown whether these periapical lesion-derived stem cells (PLDSCs) are suitable for dental pulp tissue engineering. To investigate this possibility, PLDSCs and DPSCs were isolated using the tissue outgrowth method and cultured under identical conditions. We then performed in vitro experiments to investigate their biological characteristics. Our results indicate that PLDSCs proliferate actively in vitro and exhibit similar morphology, immunophenotype and multilineage differentiation ability as DPSCs. Simultaneously, PLDSCs exhibit stronger migrative ability and express more vascular endothelial growth factor and glial cell line-derived neurotrophic factor than DPSCs, and PLDSC-derived conditioned medium was more effective in tube formation assay. The mRNA expression levels of immunomodulatory genes HLA-G, IDO and ICAM-1 were also higher in PLDSCs. However, regarding osteo/odontogenic differentiation, PLDSCs showed weaker alkaline phosphatase staining and lower calcified nodule formation compared to DPSCs, as well as lower expression of ALP, RUNX2 and DSPP, as confirmed by a quantitative RT-PCR. The osteo/odontogenic protein expression levels of DSPP, RUNX2, DMP1 and SP7 were also higher in DPSCs. The present study demonstrates that PLDSCs demonstrate potential use as seed cells for dental pulp regeneration, especially for achieving enhanced neurovascularization.

Priming strategies for controlling stem cell fate: Applications and challenges in dental tissue regeneration

Mesenchymal stromal cells (MSCs) have attracted intense interest in the field of dental tissue regeneration. Dental tissue is a popular source of MSCs because MSCs can be obtained with minimally invasive procedures. MSCs possess distinct inherent properties of self-renewal, immunomodulation, proangiogenic potential, and multilineage potency, as well as being readily available and easy to culture. However, major issues, including poor engraftment and low survival rates in vivo, remain to be resolved before large-scale application is feasible in clinical treatments. Thus, some recent investigations have sought ways to optimize MSC functions in vitro and in vivo. Currently, priming culture conditions, pretreatment with mechanical and physical stimuli, preconditioning with cytokines and growth factors, and genetic modification of MSCs are considered to be the main strategies; all of which could contribute to improving MSC efficacy in dental regenerative medicine. Research in this field has made tremendous progress and continues to gather interest and stimulate innovation. In this review, we summarize the priming approaches for enhancing the intrinsic biological properties of MSCs such as migration, antiapoptotic effect, proangiogenic potential, and regenerative properties. Challenges in current approaches associated with MSC modification and possible future solutions are also indicated. We aim to outline the present understanding of priming approaches to improve the therapeutic effects of MSCs on dental tissue regeneration.

Dental Pulp Stem Cells Derived From Adult Human Third Molar Tooth: A Brief Review

The fields of regenerative medicine and stem cell-based tissue engineering have the potential of treating numerous tissue and organ defects. The use of adult stem cells is of particular interest when it comes to dynamic applications in translational medicine. Recently, dental pulp stem cells (DPSCs) have been traced in third molars of adult humans. DPSCs have been isolated and characterized by several groups. DPSCs have promising characteristics including self-renewal capacity, rapid proliferation, colony formation, multi-lineage differentiation, and pluripotent gene expression profile. Nevertheless, genotypic, and phenotypic heterogeneities have been reported for DPSCs subpopulations which may influence their therapeutic potentials. The underlying causes of DPSCs’ heterogeneity remain poorly understood; however, their heterogeneity emerges as a consequence of an interplay between intrinsic and extrinsic cellular factors. The main objective of the manuscript is to review the current literature related to the human DPSCs derived from the third molar, with a focus on their physiological properties, isolation procedures, culture conditions, self-renewal, proliferation, lineage differentiation capacities and their prospective advances use in pre-clinical and clinical applications.

Mapping the Secretome of Dental Pulp Stem Cells Under Variable Microenvironmental Conditions

There is substantial evidence supporting the anti-inflammatory and regenerative potential of dental pulp stem cells (DPSCs) through direct cell transplantation or paracrine action. However, DPSC secretome profile remains inadequately studied. This study provides proteomic profiling of the human DPSC secretome by comparatively analysising cell lysates and respective culture supernatants (i.e. conditioned media-CM) under variable oxygen tension conditions (normoxia-20% O₂/CM_Norm vs. hypoxia 2% O₂/CM_Hyp) and/or stimulation with Tumor Necrosis Factor alpha (TNF-α). DPSC-CM samples and respective crude lysates (DPSC-CL) were collected and subjected to SDS-PAGE, followed by LC-MS/MS analysis. The identified proteins were analyzed by Gene Ontology, Reactome, and String databases. The anti-inflammatory properties of DPSC-CMs were validated via an in vitro RAW_246.7 murine macrophages model through evaluation of the expression of pro-and anti-inflammatory markers by real-time PCR. Results showed a total of 2413 proteins identified in CM_Norm, 2479 in CM_Norm+TNF-α, 1642 in CM_Hyp, and 2002 in CM_Hyp + TNF-α samples. CM_Norm contained 122 proteins statistically significantly upregulated compared to the CM_Hyp and involved in pathways related to "ECM organization", "cellular response to hypoxia", and "IL signaling". Functional network analysis showed that TGFβ1, TIMP1 and TIMP2 were key nodes among proteins significantly upregulated in the CM_Norm compared to the CM_Hyp, interacting with more than 10 proteins, each. DPSC-CM application in the in vitro RAW_246.7 model decreased the expression of pro-inflammatory markers (MMP-3, MMP-9, MMP-13, MCP-1), while increasing anti-inflammatory markers (IL-10). Overall, DPSC-CM collected under normoxic conditions is enriched with anti-inflammatory, tissue repair and regenerative factors, which prompts further investigation on its therapeutic applications.

Erythropoietin (EPO) as a Key Regulator of Erythropoiesis, Bone Remodeling and Endothelial Transdifferentiation of Multipotent Mesenchymal Stem Cells (MSCs): Implications in Regenerative Medicine

Human erythropoietin (EPO) is an N-linked glycoprotein consisting of 166 aa that is produced in the kidney during the adult life and acts both as a peptide hormone and hematopoietic growth factor (HGF), stimulating bone marrow erythropoiesis. EPO production is activated by hypoxia and is regulated via an oxygen-sensitive feedback loop. EPO acts via its homodimeric erythropoietin receptor (EPO-R) that increases cell survival and drives the terminal erythroid maturation of progenitors BFU-Es and CFU-Es to billions of mature RBCs. This pathway involves the activation of multiple erythroid transcription factors, such as GATA1, FOG1, TAL-1, EKLF and BCL11A, and leads to the overexpression of genes encoding enzymes involved in heme biosynthesis and the production of hemoglobin. The detection of a heterodimeric complex of EPO-R (consisting of one EPO-R chain and the CSF2RB β-chain, CD131) in several tissues (brain, heart, skeletal muscle) explains the EPO pleotropic action as a protection factor for several cells, including the multipotent MSCs as well as cells modulating the innate and adaptive immunity arms. EPO induces the osteogenic and endothelial transdifferentiation of the multipotent MSCs via the activation of EPO-R signaling pathways, leading to bone remodeling, induction of angiogenesis and secretion of a large number of trophic factors (secretome). These diversely unique properties of EPO, taken together with its clinical use to treat anemias associated with chronic renal failure and other blood disorders, make it a valuable biologic agent in regenerative medicine for the treatment/cure of tissue de-regeneration disorders.

Sinking Our Teeth in Getting Dental Stem Cells to Clinics for Bone Regeneration

Dental stem cells have been isolated from the medical waste of various dental tissues. They have been characterized by numerous markers, which are evaluated herein and differentiated into multiple cell types. They can also be used to generate cell lines and iPSCs for long-term in vitro research. Methods for utilizing these stem cells including cellular systems such as organoids or cell sheets, cell-free systems such as exosomes, and scaffold-based approaches with and without drug release concepts are reported in this review and presented with new pictures for clarification. These in vitro applications can be deployed in disease modeling and subsequent pharmaceutical research and also pave the way for tissue regeneration. The main focus herein is on the potential of dental stem cells for hard tissue regeneration, especially bone, by evaluating their potential for osteogenesis and angiogenesis, and the regulation of these two processes by growth factors and environmental stimulators. Current in vitro and in vivo publications show numerous benefits of using dental stem cells for research purposes and hard tissue regeneration. However, only a few clinical trials currently exist. The goal of this review is to pinpoint this imbalance and encourage scientists to pick up this research and proceed one step further to translation.

Characteristics, Classification, and Application of Stem Cells Derived from Human Teeth

Since mesenchymal stem cells derived from human teeth are characterized as having the properties of excellent proliferation, multilineage differentiation, and immune regulation. Dental stem cells exhibit fibroblast-like microscopic appearance and express mesenchymal markers, embryonic markers, and vascular markers but do not express hematopoietic markers. Dental stem cells are a mixed population with different sensitive markers, characteristics, and therapeutic effects. Single or combined surface markers are not only helpful for understanding the subpopulation of mixed stem cell populations according to cell function but also for improving the stable treatment effect of dental stem cells. Focusing on the discovery and characterization of stem cells isolated from human teeth over the past 20 years, this review outlines the effect of marker sorting on cell proliferation and differentiation ability and the assessment of the clinical application potential. Classified dental stem cells from markers and functional molecules can solve the problem of heterogeneity and ensure the efficacy of cell therapy strategies including dentistry, neurologic diseases, bone repair, and tissue engineering.

Conversion of stem cells from apical papilla into endothelial cells by small molecules and growth factors

Objectives

Recently, a new strategy has been developed to directly reprogram one cell type towards another targeted cell type using small molecule compounds. Human fibroblasts have been chemically reprogrammed into neuronal cells, Schwann cells and cardiomyocyte-like cells by different small molecule combinations. This study aimed to explore whether stem cells from apical papilla (SCAP) could be reprogrammed into endothelial cells (ECs) using the same strategy.

Materials and methods

The expression level of endothelial-specific genes and proteins after chemical induction of SCAP was assessed by RT-PCR, western blotting, flow cytometry and immunofluorescence. The in vitro functions of SCAP-derived chemical-induced endothelial cells (SCAP-ECs) were evaluated by tube-like structure formation assay, acetylated low-density lipoprotein (ac-LDL) uptake and NO secretion detection. The proliferation and the migration ability of SCAP-ECs were evaluated by CCK-8 and Transwell assay. LPS stimulation was used to mimic the inflammatory environment in demonstrating the ability of SCAP-ECs to express adhesion molecules. The in vivo Matrigel plug angiogenesis assay was performed to assess the function of SCAP-ECs in generating vascular structures using the immune-deficient mouse model.

Results

SCAP-ECs expressed upregulated endothelial-specific genes and proteins; displayed endothelial transcriptional networks; exhibited the ability to form functional tubular-like structures, uptake ac-LDL and secrete NO in vitro; and contributed to generate blood vessels in vivo. The SCAP-ECs could also express adhesion molecules in the pro-inflammatory environment and have a similar migration and proliferation ability as HUVECs.

Conclusions

Our study demonstrates that the set of small molecules and growth factors could significantly promote endothelial transdifferentiation of SCAP, which provides a promising candidate cell source for vascular engineering and treatment of ischemic diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02350-5.

Ultrafiltration and Injection of Islet Regenerative Stimuli Secreted by Pancreatic Mesenchymal Stromal Cells

The secretome of mesenchymal stromal cells (MSCs) is enriched for biotherapeutic effectors contained within and independent of extracellular vesicles (EVs) that may support tissue regeneration as an injectable agent. We have demonstrated that the intrapancreatic injection of concentrated conditioned media (CM) produced by bone marrow MSC supports islet regeneration and restored glycemic control in hyperglycemic mice, ultimately providing a platform to elucidate components of the MSC secretome. Herein, we extend these findings using human pancreas-derived MSC (Panc-MSC) as "biofactories" to enrich for tissue regenerative stimuli housed within distinct compartments of the secretome. Specifically, we utilized 100 kDa ultrafiltration as a simple method to debulk protein mass and to enrich for EVs while concentrating the MSC secretome into an injectable volume for preclinical assessments in murine models of blood vessel and islet regeneration. EV enrichment (EV+) was validated using nanoscale flow cytometry and atomic force microscopy, in addition to the detection of classical EV markers CD9, CD81, and CD63 using label-free mass spectrometry. EV+ CM was predominately enriched with mediators of wound healing and epithelial-to-mesenchymal transition that supported functional regeneration in mesenchymal and nonmesenchymal tissues. For example, EV+ CM supported human microvascular endothelial cell tubule formation in vitro and enhanced the recovery of blood perfusion following intramuscular injection in nonobese diabetic/severe combined immunodeficiency mice with unilateral hind limb ischemia. Furthermore, EV+ CM increased islet number and β cell mass, elevated circulating insulin, and improved glycemic control following intrapancreatic injection in streptozotocin-treated mice. Collectively, this study provides foundational evidence that Panc-MSC, readily propagated from the subculture of human islets, may be utilized for regenerative medicine applications.

Exosomes derived from stem cells from apical papilla promote craniofacial soft tissue regeneration by enhancing Cdc42-mediated vascularization

Background

Reconstruction of complex critical-size defects (CSD) in the craniofacial region is a major challenge, and soft tissue regeneration is crucial in determining the therapeutic outcomes of craniofacial CSD. Stem cells from apical papilla (SCAP) are neural crest-derived mesenchymal stem cells (MSCs) that are homologous to cells in craniofacial tissue and represent a promising source for craniofacial tissue regeneration. Exosomes, which contain compound bioactive compounds, are the key factors in stem cell paracrine action. However, the roles of exosomes derived from SCAP (SCAP-Exo) in tissue regeneration are not fully understood. Here, we explored the effects and underlying mechanisms of SCAP-Exo on CSD in maxillofacial soft tissue.

Methods

SCAP-Exo were isolated and identified by transmission electron microscopy and nanoparticle tracking analysis. The effects of SCAP-Exo on wound healing and vascularization were detected by measuring the wound area and performing histological and immunofluorescence analysis on the palatal gingival CSD of mice. Real-time live-cell imaging and functional assays were used to assess the effects of SCAP-Exo on the biological functions of endothelial cells (ECs). Furthermore, the molecular mechanisms of SCAP-Exo-mediated EC angiogenesis in vitro were tested by immunofluorescence staining, Western blot, and pull-down assays. Finally, in vivo experiments were carried out to verify whether SCAP-Exo could affect vascularization and wound healing through cell division cycle 42 (Cdc42).

Results

We found that SCAP-Exo promoted tissue regeneration of palatal gingival CSD by enhancing vascularization in the early phase in vivo and that SCAP-Exo improved the angiogenic capacity of ECs in vitro. Mechanistically, SCAP-Exo elevated cell migration by improving cytoskeletal reorganization of ECs via Cdc42 signalling. Furthermore, we revealed that SCAP-Exo transferred Cdc42 into the cytoplasm of ECs and that the Cdc42 protein could be reused directly by recipient ECs, which resulted in the activation of Cdc42-dependent filopodium formation and elevation in cell migration of ECs.

Conclusion

This study demonstrated that SCAP-Exo had a superior effect on angiogenesis and effectively promoted craniofacial soft tissue regeneration. These data provide a new option for SCAP-Exo to be used in a cell-free approach to optimize tissue regeneration in the clinic.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02151-w.

Angiogenesis in Regenerative Dentistry: Are We Far Enough for Therapy?

Angiogenesis is a broad spread term of high interest in regenerative medicine and tissue engineering including the dental field. In the last two decades, researchers worldwide struggled to find the best ways to accelerate healing, stimulate soft, and hard tissue remodeling. Stem cells, growth factors, pathways, signals, receptors, genetics are just a few words that describe this area in medicine. Dental implants, bone and soft tissue regeneration using autologous grafts, or xenografts, allografts, their integration and acceptance rely on their material properties. However, the host response, through its vascularization, plays a significant role. The present paper aims to analyze and organize the latest information about the available dental stem cells, the types of growth factors with pro-angiogenic effect and the possible therapeutic effect of enhanced angiogenesis in regenerative dentistry.

Effects of serum-free culture media on human apical papilla cells properties

OBJECTIVE

Aiming at more effective and safer cell therapies, the objective of this study was to evaluate the biological properties of human apical papilla cells cultured in the absence of serum supplementation in comparison to cells cultured with fetal bovine serum (FBS).

DESIGN

Two apical papilla cell populations were isolated from third molars with incomplete rhizogenesis, and cultured in four different media: minimum essential Eagle medium - alpha modification (alpha-MEM); alpha-MEM supplemented with FBS (alpha-MEM + FBS); Dulbecco's modified Eagle medium/nutrient mixture F-12 (DMEM/F12); and DMEM/F12 supplemented with FBS (DMEM/F12 + FBS). We evaluated their proliferation, clonogenicity, and in vitro osteogenic and chondrogenic differentiation potential.

RESULTS

Apical papilla cells cultured in DMEM/F12 + FBS and alpha-MEM + FBS were more proliferative than those grown in serum-free media, and also exhibited greater efficiency in colony cell formation. Despite this, all study groups showed immunostaining for the marker of mitosis anti-PHH3. Also, alpha-MEM + FBS, alpha-MEM, and DMEM/F12 + FBS exhibited higher amount of mineralized deposits in vitro than DMEM/F12, while only cells cultured with FBS were able to form spheres in chondrogenic differentiation assay.

CONCLUSIONS

Our results showed that, although the cultivation of apical papilla cells in a serum-free medium has reduced the properties of cell proliferation and differentiation, these cells are still capable of maintaining their desirable characteristics.

Proteomic profiling of various human dental stem cells - a systematic review

BACKGROUND

The proteomic signature or profile best describes the functional component of a cell during its routine metabolic and survival activities. Additional complexity in differentiation and maturation is observed in stem/progenitor cells. The role of functional proteins at the cellular level has long been attributed to anatomical niches, and stem cells do not deflect from this attribution. Human dental stem cells (hDSCs), on the whole, are a combination of mesenchymal and epithelial coordinates observed throughout craniofacial bones to pulp.

AIM

To specify the proteomic profile and compare each type of hDSC with other mesenchymal stem cells (MSCs) of various niches. Furthermore, we analyzed the characteristics of the microenvironment and preconditioning changes associated with the proteomic profile of hDSCs and their influence on committed lineage differentiation.

METHODS

Literature searches were performed in PubMed, EMBASE, Scopus, and Web of Science databases, from January 1990 to December 2018. An extra inquiry of the grey literature was completed on Google Scholar, ProQuest, and OpenGrey. Relevant MeSH terms (PubMed) and keywords related to dental stem cells were used independently and in combination.

RESULTS

The initial search resulted in 134 articles. Of the 134 full-texts assessed, 96 articles were excluded and 38 articles that met the eligibility criteria were reviewed. The overall assessment of hDSCs and other MSCs suggests that differences in the proteomic profile can be due to stem cellular complexity acquired from varied tissue sources during embryonic development. However, our comparison of the proteomic profile suffered inconsistencies due to the heterogeneity of various hDSCs. We believe that the existence of a heterogeneous population of stem cells at a given niche determines the modalities of regeneration or tissue repair. Added prominences to the differences present between various hDSCs have been reasoned out.

CONCLUSION

Systematic review on proteomic studies of various hDSCs are promising as an eye-opener for revisiting the proteomic profile and in-depth analysis to elucidate more refined mechanisms of hDSC functionalities.

Growth Factors and Small-molecule Compounds in Derivation of Endothelial Lineages from Dental Stem Cells

INTRODUCTION

Incorporating fully assembled microvascular networks into bioengineered dental pulp constructs can significantly enhance functional blood flow and tissue survival upon transplantation. Endothelial cells (ECs), cellular building blocks of vascular tissue, play an essential role in the process of prevascularization. However, obtaining sufficient ECs from a suitable source for translational application is challenging. Dental stem cells (DSCs), which exhibit a robust proliferative ability and immunocompatibility because of their autologous origin, could be a promising alternative cell source for the derivation of endothelial lineages. Under specific culture conditions, DSCs differentiate into osteo/odontogenic, adipogenic, chondrogenic, and neurogenic cell lineages.

METHODS

Recently, a new approach has been developed to directly reprogram cells using chemical cocktails and growth factors. Compared with the traditional reprogramming approach based on the forced expression of exogenous transcription factors, the chemical strategy avoids the risk associated with lentiviral transduction while offering a more viable methodology to drive cell lineage switch. The aim of this review was to unveil the concept of the use of small-molecule compounds and growth factors modulating key signaling pathways to derive ECs from DSCs.

RESULTS

In addition, our preliminary study showed that stem cells from the apical papilla could be induced into EC-like cells using small-molecule compounds and growth factors. These EC-like cells expressed endothelial specific genes (CD31 and VEGFR2) and proteins (CD31, VEGF receptor 2, and vascular endothelial cadherin) as well as gave rise to vessel-like tubular structures in vitro.

CONCLUSIONS

Our preliminary results suggest that chemical reprogramming might offer a novel way to generate EC-like cells from dental stem cells.

Ischemia-Like Stress Conditions Stimulate Trophic Activities of Adipose-Derived Stromal/Stem Cells

Adipose-derived stromal/stem cells (ASCs) have been shown to exert regenerative functions, which are mainly attributed to the secretion of trophic factors. Upon transplantation, ASCs are facing an ischemic environment characterized by oxygen and nutrient deprivation. However, current knowledge on the secretion capacity of ASCs under such conditions is limited. Thus, the present study focused on the secretory function of ASCs under glucose and oxygen deprivation as major components of ischemia. After exposure to glucose/oxygen deprivation, ASCs maintained distinct viability, but the metabolic activity was greatly reduced by glucose limitation. ASCs were able to secrete a broad panel of factors under glucose/oxygen deprivation as revealed by a cytokine antibody array. Quantification of selected factors by ELISA demonstrated that glucose deprivation in combination with hypoxia led to markedly higher secretion levels of the angiogenic and anti-apoptotic factors IL-6, VEGF, and stanniocalcin-1 as compared to the hypoxic condition alone. A conditioned medium of glucose/oxygen-deprived ASCs promoted the viability and tube formation of endothelial cells, and the proliferation and migration of fibroblasts. These findings indicate that ASCs are stimulated by ischemia-like stress conditions to secrete trophic factors and would be able to exert their beneficial function in an ischemic environment.

Exosomes Derived from Stem Cells from the Apical Papilla Promote Dentine-Pulp Complex Regeneration by Inducing Specific Dentinogenesis

Regenerative endodontic procedures (REPs) are a new option for the treatment of dental pulp or periapical diseases in permanent teeth with open apices. Histologically, the new tissues formed in the root canal after REPs are mainly cementum- or bone-like mineralised tissues, but not the real dentine-pulp complex. Therefore, how to promote dentine-pulp complex regeneration and improve the clinical effects of REPs has become a prominent research topic. Stem cells from apical papilla (SCAP) are derived from the dental papilla that can differentiate into primary odontoblasts and dental pulp cells that produce root dentine and dental pulp. Exosomes are the key regulator for the paracrine activity of stem cells and can influence the function of recipient cells. In this study, SCAP-derived exosomes (SCAP-Exo) were introduced into the root fragment containing bone marrow mesenchymal stem cells (BMMSCs) and transplanted subcutaneously into immunodeficient mice. We observed that dental pulp-like tissues were present and the newly formed dentine was deposited onto the existing dentine in the root canal. Afterwards, the effects of SCAP-Exo on the dentinogenesis of BMMSCs were elucidated in vitro. We found that the gene and protein expression of dentine sialophosphoprotein and mineralised nodule formation in BMMSCs treated with SCAP-Exo were significantly increased. In summary, SCAP-Exo were endocytosed by BMMSCs and obviously improved their specific dentinogenesis. The use of exosomes derived from dental stem cells could comprise a potential therapeutic approach for dentine-pulp complex regeneration in REPs.

Photobiomodulation effect on angiogenic proteins produced and released by dental pulp cells

OBJECTIVE

To verify the photobiomodulation effect on angiogenic proteins produced and released by dental human pulpal fibroblasts (HPFs).

MATERIAL AND METHODS

HPFs were irradiated with 660-nm low-level laser at fluences of 2.5 J/cm² and 3.7 J/cm². The control group was not irradiated. MTT, crystal violet, and ELISA assays respectively verified viability, proliferation, and angiogenic protein (supernatant/lysate) at 6 h, 12 h, and 24 h after photobiomodulation. Capillary-like structure formation assay verified functional role. Two-way ANOVA/Tukey's test and ANOVA/Bonferroni's multiple comparisons test respectively verified cell viability/proliferation and intragroup and intergroup comparisons of protein synthesis (p < 0.05).

RESULTS

Irradiated and non-irradiated HPFs showed statistically similar cell viability and proliferation pattern. Intragroup comparisons showed similar patterns of protein synthesis for all groups: VEGF-A, VEGF-C, and vascular endothelial growth factor receptor 1 (VEGFR1) increased significantly in the supernatant, while FGF-2 and VEGF-A increased significantly in the lysate. The lower fluence significantly increased BMP-9 (6 h) in the supernatant and VEGFR1 (6 h and 12 h) and VEGF-D (24 h) in the lysate, while the higher fluence significantly increased BMP-9 (6 h) in the supernatant and VEGFR1 (12 h) in the lysate. Regardless of the time, both fluences statistically downregulated placental growth factor (PLGF) and PDGF secretion. Both fluences statistically decreased VEGF-A secretion (24 h) and PLGF production (6 h).

CONCLUSION

Photobiomodulation produced stimulatory effects on angiogenic protein secretion by pulp fibroblasts. In terms of photobiomodulation, over time, both fluences significantly increased the secretion of VEGF-A, VEGF-C, and VEGFR1 and significantly upregulated BMP-9 (6 h) in the supernatant; for capillary-like structure formation, the fluence of 2.5 J/cm² was better than the fluence of 3.7 J/cm².

CLINICAL RELEVANCE

This study results addressed effective photobiomodulation parameters tailored for pulp angiogenesis.

Dental pulp stem cells from human teeth with deep caries displayed an enhanced angiogenesis potential in vitro

Background/purpose

Dental pulp stem cells can be isolated from human teeth with deep caries (cDPSCs), but their biological characteristics are still unclear. The aim of this study was to investigate the angiogenic potential of cDPSCs and compare them to dental pulp stem cells from human normal teeth (nDPSCs).

Materials and methods

Cells were isolated from human pulp tissue of normal and infected teeth with deep caries. Basic mesenchymal stem cell (MSC) characterization was conducted. Colony forming units and proliferation ability were evaluated in nDPSCs and cDPSCs. Expression of VEGF in both tissues and cells was examined by immunohistochemical staining. After stimulating nDPSCs and cDPSCs with an angiogenic medium, angiogenic markers were evaluated by qRT-PCR and western blotting. Finally, tube formation assays were used to evaluate the in vitro angiogenesis potential of both cell populations.

Results

Both nDPSCs and cDPSCs possessed typical MSC characteristics. cDPSCs had enhanced colony formation and proliferation capacities than nDPSCs did. The expression of VEGF was higher in pulp tissue from teeth with deep caries and cDPSCs than in normal tissue and nDPSCs. When both cell types were grown in vitro under angiogenic conditions, cDPSCs expressed a higher level of angiogenic markers and showed a stronger angiogenesis potential than nDPSCs did.

Conclusion

cDPSCs maintained MSC traits and presented a higher angiogenesis potential than nDPSCs.

Evaluation of growth, stemness, and angiogenic properties of dental pulp stem cells cultured in cGMP xeno-/serum-free medium

This study was aimed to investigate the effects of cGMP xeno-/serum-free medium (XSF, Irvine Scientific) on the properties of human dental pulp stem cells (DPSCs). DPSCs, from passage 2, were cultured in XSF or fetal bovine serum (FBS)-supplemented medium, and sub-cultured up to passage 8. Cumulative population doublings (PDs) and the number of colony-forming-units (CFUs) were determined. qRT-PCR, ELISA, and in vitro assays were used to assess angiogenic capacity. Flow cytometry was used to measure CD73, CD90, and CD105 expression. Differentiation into osteo-, adipo-, and chondrogenic cell lineages was performed. DPSCs showed more elongated morphology, a reduced rate of proliferation at later passages, and lower CFU counts in XSF compared with FBS. Expression of angiogenic factors at the gene and protein levels varied in the two media and with passage number, but cells grown in XSF had more in vitro angiogenic activity. The majority of early and late passage DPSCs cultured in XSF expressed CD73 and CD90. In contrast, the percentage of CD105 positive DPSCs in XSF medium was significantly lower with increased passage whereas the majority of cells cultured in FBS were CD105 positive. Switching XSF-cultured DPSCs to medium supplemented with human serum restored the expression of CD105. The tri-lineage differentiation of DPSCs cultured under XSF and FBS conditions was similar. We showed that despite reduced CD105 expression levels, DPSCs expanded in XSF medium maintained a functional MSC phenotype. Furthermore, restoration of CD105 expression is likely to occur upon in vivo transplantation, when cells are exposed to human serum.

Three-dimensional tissue engineering-based Dentin/Pulp tissue analogue as advanced biocompatibility evaluation tool of dental restorative materials

OBJECTIVE

Two-dimensional (2D) in vitro models have been extensively utilized for cytotoxicity assessment of dental materials, but with certain limitations in terms of direct in vitro-in vivo extrapolation (IVIVE). Three-dimensional (3D) models seem more appropriate, recapitulating the structure of human tissues. This study established a 3D dentin/pulp analogue, as advanced cytotoxicity assessment tool of dental restorative materials (DentCytoTool).

METHODS

DentCytoTool comprised two compartments: the upper, representing the dentin component, with a layer of odontoblast-like cells expanded on microporous membrane of a cell culture insert and covered by a treated dentin matrix; and the lower, representing a pulp analogue, incorporating HUVEC/SCAP co-cultures into collagen I/fibrin hydrogels. Representative resinous monomers (HEMA: 1-8mM; TEGDMA: 0.5-5mM) and bacterial components (LPS: 1μg/ml) were applied into the construct. Cytotoxicity was assessed by MTT and LDH assays, live/dead staining and real-time PCR for odontogenesis- and angiogenesis-related markers.

RESULTS

DentCytoTool supported cell viability and promoted capillary-like network formation inside the pulp analogue. LPS induced expression of odontogenesis-related markers (RUNX2, ALP, DSPP) without compromising viability of the odontoblast-like cells, while co-treatment with LPS and resin monomers induced cytotoxic effects (live/dead staining, MTT and LDH assays) in cells of both upper and lower compartments and reduced expression angiogenesis-related markers (VEGF, VEGFR2, ANGPT-1, Tie-2, PECAM-1) in a concentration- and time- dependent manner. LPS treatment aggravated TEGDMA-induced and -in certain concentrations (2-4mM)- HEMA-induced cytotoxicity.

SIGNIFICANCE

DentCytoTool represents a promising tissue-engineering-based cytotoxicity assessment tool, providing more insight into the mechanistic aspects of interactions of dental materials to the dentin/pulp complex.

In situ prevascularization designed by laser-assisted bioprinting: effect on bone regeneration

Vascularization plays a crucial role in bone formation and regeneration process. Development of a functional vasculature to improve survival and integration of tissue-engineered bone substitutes remains a major challenge. Biofabrication technologies, such as bioprinting, have been introduced as promising alternatives to overcome issues related to lack of prevascularization and poor organization of vascular networks within the bone substitutes. In this context, this study aimed at organizing endothelial cells in situ, in a mouse calvaria bone defect, to generate a prevascularization with a defined architecture, and promote in vivo bone regeneration. Laser-assisted bioprinting (LAB) was used to pattern Red Fluorescent Protein-labeled endothelial cells into a mouse calvaria bone defect of critical size, filled with collagen containing mesenchymal stem cells and vascular endothelial growth factor. LAB technology allowed safe and controlled in vivo printing of different cell patterns. In situ printing of endothelial cells gave rise to organized microvascular networks into bone defects. At two months, vascularization rate (vr) and bone regeneration rate (br) showed statistically significant differences between the 'random seeding' condition and both 'disc' pattern (vr = +203.6%; br = +294.1%) and 'crossed circle' pattern (vr = +355%; br = +602.1%). These results indicate that in vivo LAB is a valuable tool to introduce in situ prevascularization with a defined configuration and promote bone regeneration.

Angiogenic properties of dental pulp stem cells conditioned medium on endothelial cells in vitro and in rodent orthotopic dental pulp regeneration

Objectives

To evaluate the effect of SHED-CM on the proliferation, differentiation, migration ability, cell death, gene expression and production of VEGF of HUVEC in vitro and in a rodent orthotopic dental pulp regeneration.

Methods

Three culture media [M199, DMEM/Ham's F12 and DMEM/Ham's F12 conditioned by SHEDs] were used as experimental groups. SHED-CM was prepared maintaining confluent cells in culture without serum for 3 days. The proliferation and cell death marker of HUVECs were assessed using flow cytometry. The capacity of formation of vascular-like structures was analyzed in cells grown over Matrigel^® in hypoxic condition. HUVECs migration was followed using the scratch test. VEGF-A expression in HUVECs was assessed using real time RT-qPCR; and VEGF synthesis with ELISA test. SHED-CM was also applied in rodent ortotopic model of dental pulp regeneration in rats. The formed tissue was submitted to histological and immunohistochemical analyses.

Results

SHED-CM promoted significantly lower expression of 7AAD in HUVECs; whereas the expression of the Ki67 was similar in all groups. The vascular-like structures were observed in all groups. Migration of SHED-CM group was faster than DMEM/Ham's F12. SHED-CM induced similar expression of VEGF-A than M199, and higher than DMEM/Ham's F12. SHED-CM induced significantly higher VEGF synthesis than other media. SHED-CM induced formation of a vascularized connective tissue inside the root canal.

Conclusion

The study showed that SHEDs release angiogenic and cytoprotective factors, which are of great importance for tissue engineering.

Clinical significance

SHED-CM could be an option to the use of stem cells in tissue engineering.

Restoring In Vivo-Like Membrane Lipidomics Promotes Exosome Trophic Behavior from Human Placental Mesenchymal Stromal/Stem Cells

Human mesenchymal stem cells (hMSCs) are an effective tool in regenerative medicine notably for their intrinsic plentiful paracrine activity rather than differentiating properties. The hMSC secretome includes a wide spectrum of regulatory and trophic factors, encompassing several naked molecules as well as different kinds of extracellular vesicles (EVs). Among EVs, exosomes represent an intriguing population, able to shuttle proteins, transcription factors, and genetic materials, with a relevant role in cell-to-cell communication, modulating biological responses in recipient cells. In this context, the extracellular milieu can greatly impact the paracrine activity of stem cells, modifying their metabolism, and the dynamics of vesicle secretion. In the present study, we investigated the effects elicited on exosome patterning by tailored, ad hoc formulated lipid supplementation (Refeed^®) in MSCs derived from human fetal membranes (hFM-MSCs). Wound healing experiments revealed that stem cell exposure to exosomes obtained from Refeed^®-supplemented hFM-MSCs increased their migratory capability, although the amount of exosomes released after Refeed^® supplementation was lower than that yielded from non-supplemented cells. We found that such a decrease was mainly due to a different rate of exosomal exocytosis rather than to an effect of the lipid supplement on the endocytic pathway. Endoplasmic reticulum homeostasis was modified by supplementation, through the upregulation of PKR-like ER kinase (PERK) and inositol-requiring enzyme 1α (IRE1α). Increased expression of these proteins did not lead to stress-induced, unfolded protein response (UPR)-mediated apoptosis, nor did it affect phosphorylation of p38 kinase, suggesting that PERK and IRE1α overexpression was due to augmented metabolic activities mediated by optimization of a cellular feeding network afforded through lipid supplementation. In summary, these results demonstrate how tailored lipid supplementation can successfully modify the paracrine features in hFM-MSCs, impacting both intracellular vesicle trafficking and secreted exosome number and function.

A Novel Approach to Septal Perforation Repair: Septal Cartilage Cells Induce Chondrogenesis of hASCs In Vitro

The aim of this study was to investigate the effect of medium harvested from septal cartilage cells on chondrogenic differentiation of adipose stem cells (hASCs) and to compare/contrast its properties to those of a commonly used standard medium formulation in terms of induction and maintenance of chondrogenic hASCs. Differentiation was carried out under three different conditions: septal cartilage medium-SCM, chondrogenic differentiation medium-CM, and 50:50 mixture of CM/SCM. Mesenchymal stem cells (MSCs) markers were determined by flow cytometry. The cytotoxic and apoptotic effects were determined by MTS and Annexin V assay, respectively. The differentiation status of the cells was confirmed by Alcian blue staining, and quantitative real-time flow cytometry showed that hASCs were positive for MSCs, negative for hematopoietic stem cells and endothelial cell surface markers. According to MTS analysis, the first condition was not toxic at any concentration tested. Annexin V assay revealed that the application of different concentrations of SCM did not result in any cell death. The Alcian blue and gene expression analyses showed that the cells in the SCM group underwent the highest cartilage cell formation. The observed increase in chondrogenesis may offer better treatment options for the cartilage defects seen in nasal septum perforation.

Stem Cells from the Apical Papilla: A Promising Source for Stem Cell-Based Therapy

Stem cells are biological cells that can self-renew and can differentiate into multiple cell lineages. Stem cell-based therapy is emerging as a promising alternative therapeutic option for various disorders. Mesenchymal stem cells (MSCs) are multipotent adult stem cells that are isolated from various tissues and can be used as an alternative to embryonic stem cells. Stem cells from the apical papilla (SCAPs) are a novel population of MSCs residing in the apical papilla of immature permanent teeth. SCAPs present the characteristics of expression of MSCs markers, self-renewal, proliferation, migration, differentiation, and immunosuppression, which support the application of SCAPs in stem cell-based therapy, including the immunotherapy and the regeneration of dental tissues, bone, neural, and vascular tissues. In view of these properties and therapeutic potential, SCAPs can be considered as promising candidates for stem cell-based therapy. Thus the aim of our review was to summarize the current knowledge of SCAPs considering isolation, characterization, and multilineage differentiation. The prospects for their use in stem cell-based therapy were also discussed.

Impaired angiogenic differentiation of dental pulp stem cells during exposure to the resinous monomer triethylene glycol dimethacrylate

OBJECTIVE

Dental pulp stem cells (DPSCs) can differentiate into tissue specific lineages to support dental pulp regeneration after injuries. Triethylene glycol dimethacrylate (TEGDMA) is a widely used co-monomer in restorative dentistry with adverse effects on cellular metabolism. Aim of this study was to analyze the impact of TEGDMA on the angiogenic differentiation potential of DPSCs.

METHODS

DPSCs were characterized by flow cytometry. Short-term (max. 72h) cytotoxicity of TEGDMA was assessed by MTT assay. To evaluate TEGDMA effects on angiogenic differentiation, DPSCs were cultivated in angiogenic differentiation medium (ADM) in the presence or absence of short-term non-toxic TEGDMA concentrations (0.1mM and 0.25mM). Subsequently, angiogenic differentiation was analyzed by qRT-PCR analysis of mRNA markers and in vitro spheroid sprouting assays.

RESULTS

DPSCs treated with 0.25mM TEGDMA revealed downregulation of angiogenesis-related marker genes PECAM1 (max. 3.8-fold), VEGF-A (max. 2.4-fold) and FLT1 (max. 2.9-fold) compared to respective untreated control. In addition, a reduction of the sprouting potential of DPSCs cultured in the presence of 0.25mM TEGDMA was detectable. Larger spheroidal structures were detectable in the untreated control in comparison to cells treated with 0.25mM TEGDMA. In contrast, TEGDMA at 0.1mM was not affecting angiogenic potential in the investigated time period (up to 28 days).

SIGNIFICANCE

The results of the present study show that TEGDMA concentration dependently impair the angiogenic differentiation potential of DPSCs and may affect wound healing and the formation of granulation tissue.

A Mesenchymal stem cell line (B10) increases angiogenesis in a rat MCAO model

A human mesenchymal stem cell line (B10) transplantation has been shown to improve ischemia-induced neurological deficits in animal stroke models. To understand the underlying mechanism, we have investigated the effects of B10 transplantation on cerebral angiogenesis in a rat middle cerebral artery occlusion (MCAO) model. B10 cells were transplanted intravenously 24 h after MCAO. Immunofluorescence staining results showed that compared to PBS-groups, vWF positive vessel and endoglin positive new vessels were increased in B10-transplanted MCAO groups in the lesion areas. The mRNA of angiogenesis factors including placental growth factor and hypoxia inducible factor (HIF)-1α were increased 3 days after MCAO in the core and IBZ areas of B10-transplanted group. Angiopoetin1 mRNA was increased only in the IBZ. Western blotting results showed that HIF-1α and vascular endothelial growth factor (VEGF) proteins were increased in B10-transplanted group. Both HIF-1α and VEGF were expressed in macrophage/microglia in the core area. In the IBZ, however, HIF-1α was expressed both in astrocytes and macrophage/microglia, while VEGF was expressed only in macrophage/microglia. Moreover, TGFβ protein levels were found to be increased in B10-transplanted group in the core and IBZ regions. Cell culture experiments using a human microglia cell line (HMO6) and B10 showed that IL-1β induced VEGF mRNA expression in both cell types. IL-1β was found to be highly expressed in B10 cells, and its co-culture with HMO6 further increased that in B10. Co-culture increased VEGF mRNA in both B10 and HMO6. In the rat brains, IL-1β was expressed in macrophage/microglia and transplanted-B10 cells in the core. IL-1β positive cell number was increased slightly, but significantly in B10-transplanted rats. To explore further, IL-1β expression was silenced in B10 cells by transfecting mRNA specific siRNA, and then transplanted in MCAO rats. Immunostaining result showed that endoglin positive area was decreased in IL-1β-silenced B10 transplanted groups compared to nonsilenced-B10 transplanted groups. Interestingly, vessel-like structure appeared as early as 3 days after MCAO in IL-1β-silenced B10-transplanted group. Thus our results demonstrated that B10 cells increased angiogenesis in MCAO rat model, through the regulation of HIF-1α and VEGF expression, where IL-1β might play a role.

Hepatocyte growth factor promotes the proliferation of human embryonic stem cell derived retinal pigment epithelial cells

Research that pertains to the molecular mechanisms involved in retinal pigment epithelial (RPE) development can significantly contribute to cell therapy studies. The effects of periocular mesenchymal cells on the expansion of RPE cells remain elusive. We have examined the possible proliferative role of hepatocyte growth factor (HGF) as a mesenchymal cell secretory factor against human embryonic stem cell derived RPE (hESC-RPE). We found that the conditioned medium of human mesenchymal stem cells from apical papilla and/or exogenous HGF promoted proliferation of the hESC-RPE cells as single cells and cell sheets, in addition to rabbit RPE sheets in vitro. Blockage of HGF signaling by HGF receptor inhibitor, PHA-665752, inhibited proliferation of hESC-RPE cells. However, differentiation of hESCs and human-induced pluripotent stem cells to a rostral fate and eye-field specification was unaffected by HGF. Our in vivo analysis showed HGF expression in periocular mesenchymal cells after optic cup formation in chicken embryos. Administration of HGF receptor inhibitor at this developmental stage in chicken embryos led to reduced eye size and disorganization of the RPE sheet. These findings suggested that HGF administration could be beneficial for obtaining higher numbers of hESC-RPE cells in human preclinical and clinical trials.

Erythropoietin (rhEPOa) promotes endothelial transdifferentiation of stem cells of the apical papilla (SCAP)

OBJECTIVE

Mesenchymal stem cells (MSCs) have attracted worldwide attention for their capacity to repair damaged tissue, immunosuppression, ability to differentiate into several cell types and their secretome. Earlier studies have demonstrated their angiogenic potential in vitro and in vivo. However, little is known regarding pro-angiogenic inducers of stable endothelial transdifferentiation of MSCs. Here, we employed human MSCs from the Apical Papilla (SCAP) and investigated whether recombinant human erythropoietin-alpha (rhEPOa) could act as such inducer.

DESIGN

Cultured SCAP cells were exposed to rhEPOa and assessed for cell growth kinetics, viability and morphology, as well as their capacity to form capillary tubule structures in selected microenvironments. RT-PCR was used to monitor endothelial markers and activation of EPO/EPOR pathway signaling components; while gelatin zymographies to assess activation of MMP-2.

RESULTS

rhEPOa treatment initially (48 h) accelerated cell proliferation and allowed SCAP to sprout micro-tubular structures. Morphological and biochemical differentiation was accompanied by activation of MMP-2 and upregulation of PECAM-1, VEGFR2, vWF and VE-cadherin/CDH5. SCAP expressed the cognate EPO-R, while rhEPOa-treated SCAP exhibited higher expression of molecules involved in EPO/EPOR pathway (EPOR and JAK2).

CONCLUSION

rhEPOa is capable of promoting endothelial transdifferentiation of SCAP which may be of clinical value in treating of ischemic disorders.

Stem Cells From the Apical Papilla (SCAP) as a Tool for Endogenous Tissue Regeneration

Stem cells extracted from developing tissues possibly exhibit not only unique but also superior traits against their developed counterparts. Indeed, stem cells from the apical papilla (SCAP); a unique group of dental stem cells related to developing roots have been shown to be a promising tool for regenerative endodontic procedures and regeneration in general. Studies have characterized the phenotypic traits as well as other regenerative potentials of these cells. Specific sub-populations have been highlighted as well as their neurogenic and angiogenic properties. Nevertheless, in light of the previously discussed features and potential applications of SCAP, there is still much to understand and a lot of information to unravel. The current review will discuss the role of specific markers for detection of different functional populations of SCAP; including CD146 and STRO-1, as well as their true multilineage differentiation potential. In particular, the role of the secretome in association with paracrine signaling in inflammatory microenvironments is also tackled. Additionally, the role of SCAP both in vitro and in vivo during regenerative approaches and in response to different growth factors and biologic scaffolds is highlighted. Finally, this review will shed light on current knowledge regarding the clinical translational potential of SCAP and elucidate possible areas for future research applications.