Label-free quantitative proteomic analysis of human periodontal ligament stem cells by high-resolution mass spectrometry

Influence of Hypoxic Condition on Cytotoxicity, Cellular Migration, and Osteogenic Differentiation Potential of Aged Periodontal Ligament Cells

OBJECTIVE

 This study aimed to investigate and compare the influence of hypoxic conditions on cytotoxicity, cellular migration, and osteogenic differentiation of aged periodontal ligament (PDL) cells.

MATERIALS AND METHODS

 Isolated human PDL cells from aged and young subjects were cultured under hypoxic conditions, which were treated with hydrogen peroxide (H2O2) (0, 25, 50, 100, 200, and 500 µM). To assess cytotoxicity, lactate dehydrogenase release was determined by the optical density at 490 nm, and the percentage of cell death was calculated. An in vitro wound healing assay was performed over 24 to 48 hours for cellular migration determination. Osteogenic differentiation was determined by alizarin red staining and osteogenic gene expression, including the expression of runt-related transcription factor 2 (RUNX2), alkaline phosphatase (ALP), and osteopontin (OPN).

RESULTS

 There was a significant difference in the percentage of cell death with high hypoxic condition (200 and 500 µM) compared to low hypoxic conditions on both day 1 and 2. The highest cellular migration was depicted at 50 µM in both young and aged groups of the in vitro wound healing assay. Osteogenic gene expression of RUNX2 in the aged group was increased at 25 and 50 µM hypoxic condition at day 7, but the expression was gradually decreased after 14 days. On the contrary, the expression of ALP and OPN in the aged group was increased at day 14. Only OPN had been found to be statistically significantly different when compared with gene expression at day 7 and 14 (p < 0.05). The results showed no statistically significant differences when compared with the young and aged groups in all genes and all concentrations.

CONCLUSION

 The concentration of low hypoxic condition (25-50 µM) was proposed to promote cell viability, cellular migration, and osteogenic differentiation in aged PDL cells. We suggested that the potential of aged PDL cells for use in cell therapy for periodontal regeneration might possibly be similar to that of young PDL cells.

Comparison of Periodontal Ligament Stem Cells with Mesenchymal Stem Cells from Other Sources: A Scoping Systematic Review of In vitro and In vivo Studies

OBJECTIVE

The application of stem cells in regenerative medicine depends on their biological properties. This scoping review aimed to compare the features of periodontal ligament stem cells (PDLSSCs) with stem cells derived from other sources.

DESIGN

An electronic search in PubMed/Medline, Embase, Scopus, Google Scholar and Science Direct was conducted to identify in vitro and in vivo studies limited to English language.

RESULTS

Overall, 65 articles were included. Most comparisons were made between bone marrow stem cells (BMSCs) and PDLSCs. BMSCs were found to have lower proliferation and higher osteogenesis potential in vitro and in vivo than PDLSCs; on the contrary, dental follicle stem cells and umbilical cord mesenchymal stem cells (UCMSCs) had a higher proliferative ability and lower osteogenesis than PDLSCs. Moreover, UCMSCs exhibited a higher apoptotic rate, hTERT expression, and relative telomerase length. The immunomodulatory function of adipose-derived stem cells and BMSCs was comparable to PDLSCs. Gingival mesenchymal stem cells showed less sensitivity to long-term culture. Both pure and mixed gingival cells had lower osteogenic ability compared to PDLSCs. Comparison of dental pulp stem cells (DPSCs) with PDLSCs regarding proliferation rate, osteo/adipogenesis, and immunomodulatory properties was contradictory; however, in vivo bone formation of DPSCs seemed to be lower than PDLSCs.

CONCLUSION

In light of the performed comparative studies, PDLSCs showed comparable results to stem cells derived from other sources; however, further in vivo studies are needed to determine the actual pros and cons of stem cells in comparison to each other.

The Role of Extracellular Vesicles in Optic Nerve Injury: Neuroprotection and Mitochondrial Homeostasis

Stem cell therapies hold great promise as alternative treatments for incurable optic nerve disorders. Although mesenchymal stem cells exhibit various tissue regeneration and recovery capabilities that may serve as valuable therapies, the clinical applications remain limited. Thus, we investigated the utility of extracellular vesicles (EVs) from human placenta-derived mesenchymal stem cells (hPSCs) in this context. Hypoxically preconditioned hPSCs (HPPSCs) were prepared via short-term incubation under 2.2% O2 and 5.5% CO2. The EVs were then isolated. R28 cells (retinal precursor cells) were exposed to CoCl2 and treated with EVs for 24 h. Cell proliferation and regeneration were measured using a BrdU assay and immunoblotting; ATP quantification revealed the extent of the mitochondrial function. The proteome was determined via liquid chromatography-tandem mass spectroscopy. Differentially expressed proteins (DEPs) were detected and their interactions identified. HPPSC_EVs functions were explored using animal models of optic nerve compression. HPPSC_EVs restored cell proliferation and mitochondrial quality control in R28 cells damaged by CoCl2. We identified DEPs (p < 0.05) that aided recovery. The mitochondrial DEPs included LONP1; PARK7; VDAC1, 2, and 3; HSPD1; and HSPA9. EVs regulated the levels of mitophagic proteins in R28 cells injured by hypoxia; the protein levels did not increase in LONP1 knockdown cells. LONP1 is a key mediator of the mitophagy that restores mitochondrial function after hypoxia-induced optic nerve injury.

mTOR is involved in LRP5-induced osteogenic differentiation of normal and aged periodontal ligament stem cells in vitro

Periodontal ligament stem cells (PDLSCs) plays an important role in tissue engineering. As the age increased, the cell viability and osteogenic differentiation of PDLSCs all decreased. Low density lipoprotein receptor related protein 5 (LRP5) was found to promote bone marrow mesenchymal stem cells osteogenic differentiation. Therefore, our study explored the effect of LRP5 on normal and aged PDLSCs and relative mechanism. Here, we found that the expression of LRP5 in PDLSCs of 24 week-old mice was decreased compared with PDLSCs of 5 week-old mice (n = 5). . LRP5 overexpression in PDLSCs increased the intensity of alkaline phosphatase and alizarin red staining, accompanied with upregulated the levels of RUNX family transcription factor 2, collagen type I, and β-Catenin. LRP5 knockdown displayed the opposite results in PDLSCs in vitro. LRP5 overexpression in aged PDLSCs restored part ability of osteogenic differentiation. Meantime, LRP5 increased the protein expression of phosphorylation of mammalian target of rapamycin (p-mTOR) in normal and aged PDLSCs. Immunofluorescence showed that LRP5 increased the accumulation of p-mTOR nucleus. The effect of LRP5 in promoting osteogenic differentiation of PDLSCs can be antagonized by mTOR inhibitor rapamycin. These findings suggest that LRP5 positively regulate osteogenic differentiation of normal and aged PDLSCs and may be a potential target for enlarging the application of PDLSCs in tissue regeneration.

Influence of surface termination of ultrananocrystalline diamond films coated on titanium on response of human osteoblast cells: A proteome study

Successful osseointegration, i.e. the fully functional connection of patient's bone and artificial implant depends on the response of the cells to the direct contact with the surface of the implant. The surface properties of the implant which trigger cell responses leading to its integration into the surrounding bone can be tailored by surface modifications or coating with thin layers. One potential material for such applications is ultrananocrystalline diamond (UNCD). It combines the exceptional mechanical properties of diamond with good biocompatibility and possibility of coating as thin uniform films on different substrates of biological interest. In the current work we firstly deposited UNCD films on titanium-coated substrates and applied oxygen or ammonia plasma to modify their surface properties. The as-grown and modified UNCD exhibited relatively smooth surfaces with topography dominated by rounded features. The modifications induced oxygen- or amino-terminated surfaces with increased hydrophilicity. In addition, the UNCD coatings exhibited very low coefficient of friction when diamond was used as a counterpart. As-grown and modified UNCD samples were applied to study the responses of human osteoblast MG63 cells triggered by surfaces with various terminations assessed by proteomic analysis. The results revealed that the coating of Ti with UNCD as well as the plasma modifications resulting in O- or NH₂-terminated UNCD induced upregulation of proteins specific for cytoskeleton, cell membrane, and extracellular matrix (ECM) involved in the cell-ECM-surface interactions. Proteins from each of these groups, namely, vimentin, cadherin and fibronectin were further studied immunocytochemically and the results confirmed their increased abundance leading to improved cell-to-surface adhesion and cell-to-cell interactions. These findings demonstrate the potential of implant coating with UNCD and its surface modifications for better osseointegration and bone formation.

Proteomic profile of human stem cells from dental pulp and periodontal ligament

Background The study of molecular profiling of dental pulp stem cells (DPSCs) and periodontal ligament stem cells (PDLSCs) contributes to understanding the high proliferation ability and multi-lineage differentiation potential. Objectives The aim of the study was to compare the protein abundance and specific markers of DPSCs and PDLSCs by protein profiles. Material and methods The DPSCs and PDLSCs extracted from the same tooth were lysed with 3 biological replicates and the protein was collected. Two-dimensional electrophoresis technology and TMT proteomics were used to separate and identify proteins. The data are available via ProteomeXchange with identifier PXD021997. The RT-qPCR detection of mRNA expression revealed a special marker for distinguishing two kinds of dental stem cells. Results Compared with PDLSCs, 962 differential proteins (DAPs) were up-regulated, and 127 were down-regulated in DPSCs. In the up-regulated DAPs, two high-scoring sub-networks were detected for neural-related molecules, which encode cell vesicle transport and mitochondrial energy transfer to regulate cell proliferation and secretion factors. A large number of cell adhesion molecules were distinguished among the highly expressed molecules of PDLSCs, supporting that stem cells provide cell attachment functions. It was interpreted ENPL, HS90A and HS90B were highly expressed in DPSCs, while CKB was highly abundant in PDLSCs. Another cell group confirmed that these molecules can be used as special biomarkers to identify and distinguish between DPSCs and PDLSCs. Conclusions This study can promote the basic research and clinical application of dental stem cells. Significance The high-throughput protein profiles were tested by combining two-dimensional gel proteomics and TMT-based proteomics. The proteomics of DPSCs and PDLSCs without individual difference demonstrated an accurate and comprehensive molecular expression profiles and interpretation of neural application potential, this study promotes the basic research of dental stem cells and clinical application.

UBA2 activates Wnt/β-catenin signaling pathway during protection of R28 retinal precursor cells from hypoxia by extracellular vesicles derived from placental mesenchymal stem cells

Background

Stem cell transplantation has been proposed as an alternative treatment for intractable optic nerve disorders characterized by irrecoverable loss of cells. Mesenchymal stem cells, with varying tissue regeneration and recovery capabilities, are being considered for potential cell therapies. To overcome the limitations of cell therapy, we isolated exosomes from human placenta-derived mesenchymal stem cells (hPMSCs) and investigated their therapeutic effects in R28 cells (retinal precursor cells) exposed to CoCl₂.

Method

After 9 h of exposure to CoCl₂, the hypoxic damaged R28 cells were divided into the non-treatment group (CoCl₂ + R28 cells) and treatment group (CoCl₂ + R28 cells treated with exosome). Immunoblot analysis was performed for Pcna, Hif-1α, Vegf, Vimentin, Thy-1, Gap43, Ermn, Neuroflament, Wnt3a, β-catenin, phospo-GSK3β, Lef-1, UBA2, Skp1, βTrcp, and ubiquitin. The proteomes of each group were analyzed by liquid chromatography/tandem mass (LC-MS/MS) spectrometry. Differentially expressed proteins (DEPs) were detected by label-free quantification, and the interactions of the proteins were examined through signal transduction pathway and gene ontology analysis.

Result

We observed that exosome could significantly recover proliferation damaged by CoCl₂ treatment. In addition, the treatment group presented the decreased expression of Hif-1α protein (P < 0.05) and increased expression of proliferation marker, Pcna, and nerve regeneration-related factors such as Vimentin, Thy-1, and Neuroflament (P < 0.05) compared with the non-treatment group. In total, 200 DEPs were identified in the non-treatment group and treatment group (fold change ≥ 2, p < 0.05). Catenin and ubiquitin systems (UBA2, UBE2E3, UBE2I) were found in both the DEP lists of downregulated proteins from the non-treatment group and upregulated proteins from the treatment group. The mRNA expressions of ubiquitin systems were significantly decreased under hypoxic conditions. Moreover, UBA2 and Wnt/β-catenin protein were associated with the rescue of the hypoxic damaged R28 cells. Using a siRNA system, we could find it out that hPMSC exosomes could not repair altered expressions of target proteins by CoCl₂ in lacking UBA2 R28 cells.

Conclusion

This study reported that hypoxic damaged expression of regeneration markers in R28 cells was significantly recovered by hPMSC exosomes. We could also demonstrate that UBA2 played a key role in activating the Wnt/β-catenin signaling pathway during protection of hypoxic damaged R28 cells, induced by hPMSC exosomes.

Biomimetic titanium implant coated with extracellular matrix enhances and accelerates osteogenesis

Aim: To evaluate the biological function of titanium implants coated with cell-derived mineralized extracellular matrix, which mimics a bony microenvironment. Materials & methods: A biomimetic titanium implant was fabricated primarily by modifying the titanium surface with TiO₂ nanotubes or sand-blasted, acid-etched topography, then was coated with mineralized extracellular matrix constructed by culturing bone marrow mesenchymal stromal cells. The osteogenic ability of biomimetic titanium surface in vitro and in vivo were evaluated. Results: In vitro and in vivo studies revealed that the biomimetic titanium implant enhanced and accelerated osteogenesis of bone marrow stromal cells by increasing cell proliferation and calcium deposition. Conclusion: By combining surface topography modification with biological coating, the results provided a valuable method to produce biomimetic titanium implants with excellent osteogenic ability.

Aggregation-induced integrated stress response rejuvenates culture-expanded human mesenchymal stem cells

Protein homeostasis is critical for cellular function, as loss of homeostasis is attributed to aging and the accumulation of unwanted proteins. Human mesenchymal stem cells (MSCs) have shown promising therapeutic potential due to their impressive abilities to secrete inflammatory modulators, angiogenic, and regenerative cytokines. However, there exists the problem of human MSC expansion with compromised therapeutic quality. Duringin vitro expansion, human MSCs are plated on stiff plastics and undergo culture adaptation, which results in aberrant proliferation, shifts in metabolism, and decreased autophagic activity. It has previously been shown that three-dimensional (3D) aggregation can reverse some of these alterations by heightening autophagy and recovering the metabolic state back to a naïve phenotype. To further understand the proteostasis in human MSC culture, this study investigated the effects of 3D aggregation on the human MSC proteome to determine the specific pathways altered by aggregation. The 3D aggregates and 2D cultures of human MSCs derived from bone marrow (bMSC) and adipose tissue (ASC) were analyzed along with differentiated human dermal fibroblasts (FB). The proteomics analysis showed the elevated eukaryotic initiation factor 2 pathway and the upregulated activity of the integrated stress response (ISR) in 3D aggregates. Specific protein quantification further determined that bMSC and ASC responded to ISR, while FB did not. 3D aggregation significantly increased the ischemic survival of bMSCs and ASCs. Perturbation of ISR with small molecules salubrinal and GSK2606414 resulted in differential responses of bMSC, ASC, and FB. This study indicates that aggregation-based preconditioning culture holds the potential for improving the therapeutic efficacy of expanded human MSCs via the establishment of ISR and homeostasis.