Mineralization and expression of Col1a1-3.6GFP transgene in primary dental pulp culture

Bifunctional Labeling of Rabbit Mesenchymal Stem Cells for MR Imaging and Fluorescence Microscopy

PURPOSE

Longitudinal imaging studies are important in the translational process of stem cell-based therapies. Small animal imaging models are widely available and practical but insufficiently depict important morphologic detail. In contrary, large animal models are logistically challenging and costly but offer greater imaging quality. In order to combine the advantages of both, we developed an intermediate-sized rabbit animal model for cartilage imaging studies.

PROCEDURES

Rabbit mesenchymal stem cells (rMSC) were isolated as primary cultures from the bone marrow of New Zealand white rabbits. rMSC were subsequentially transduced lentivirally with eGFP and magnetically labeled with the iron oxide ferucarbotran. eGFP expression was evaluated by flow cytometry and iron uptake was analyzed by isotope dilution mass spectrometry and Prussian blue staining. Fluorescence microscopy of eGFP-transduced rMSC was performed. Viability and induction of apoptosis were assessed by XTT and caspase-3/-7 measurements. The chondrogenic potential of labeled cells was quantified by glycosaminoglycan contents in TGF-β3 induced pellet cultures. Labeled and unlabeled cells underwent magnetic resonance imaging (MRI) at 1.5 T before and after differentiation using T1-, T2-, and T2*-weighted pulse sequences. Relaxation rates were calculated. rMSCs were implanted in fibrin clots in osteochondral defects of cadaveric rabbit knees and imaged by 7 T MRI. T2* maps were calculated. Statistical analyses were performed using multiple regression models.

RESULTS

Efficiency of lentiviral transduction was greater than 90 %. Fluorescence signal was dose dependent. Cellular iron uptake was significant for all concentrations (p < 0.05) and dose dependent (3.3-56.5 pg Fe/cell). Labeled rMSC showed a strong, dose-dependent contrast on all MR pulse sequences and a significant decrease in T2 and T2* relaxation rates. Compared with non-transduced or unlabeled controls, there were no adverse effects on cell viability, rate of apoptosis, or chondrogenic differentiation. MRI of labeled rMSCs in osteochondral defects showed a significant signal of the transplant with additional high-resolution anatomical information.

CONCLUSIONS

This intermediate-sized rabbit model and its bifunctional labeling technique allow for improved depiction of anatomic detail for noninvasive in vivo rMSC tracking with MRI and for immunohistological correlation by fluorescence microscopy.

Comparative proteomic profiling of human dental pulp stem cells and periodontal ligament stem cells under in vitro osteogenic induction

OBJECTIVE

This study aimed to compare the proteomic profiling of human dental pulp stem cells (DPSCs) and periodontal ligament stem cells (PDLSCs) under in vitro osteogenic induction, which imitates the microenvironment during osteo-/odontogenesis of DPSCs and PDLSCs.

DESIGN

The proteomic profiles of osteoinduced DPSCs and PDLSCs from a single donor were compared using the isobaric tag for relative and absolute quantitation (iTRAQ) technique and subsequent bioinformatics analysis.

RESULTS

A total of 159 differentially expressed proteins in PDLSCs and DPSCs were identified, 82 of which had a higher expression level in PDLSCs, while 77 were more highly expressed in DPSCs. Among these enriched proteins, certain members from the collagen, heat shock protein and protein S100 families may distinguish osteoinduced PDLSCs and DPSCs. Gene ontology (GO) classification revealed that a large number of the enriched terms distinguishing PDLSCs and DPSCs are involved in catalytic activity, protein binding, regulation of protein metabolic processes and response to stimulus. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated several involved pathways, including the fatty acid biosynthesis pathway, pantothenate and CoA biosynthesis pathway, arachidonic acid metabolism pathway and PPAR signaling pathway. Further verification showed that the mineralization and migration capacities of PDLSCs were greater than those of DPSCs, in which heat shock protein beta-1, Protein S100-A10 and S100-A11 may play a part.

CONCLUSIONS

Less than 5% of the differentially expressed proteins make up the comparative proteomic profile between osteoinduced PDLSCs and DPSCs. This study helps to characterize the differences between osteoinduced PDLSCs and DPSCs in vitro.

Enhanced differentiation of dental pulp cells cultured on microtubular polymer scaffolds in vitro

Dental caries (tooth decay) is the most common chronic disease. Dental tissue engineering is a promising alternative approach to alleviate the shortcomings of the currently available restorative materials. Mimicking the natural extracellular matrix (ECM) could enhance the performance of tissue engineering scaffolds. In this study, we developed microtubular (~20 μm diameter) polymethyl methacrylate (PMMA) scaffolds resembling the tubular (~2.5 μm diameter) structure of dentin, the collagen-based mineralized tissue that forms the major portion of teeth, to study the effect of scaffold architecture on differentiation of mouse dental pulp cells in vitro. Flat (control), plasma-treated solid and microtubular PMMA scaffolds with densities of 240±15, 459±51 and 480±116 tubules/mm2 were first characterized using scanning electron microscopy and contact angle measurements. Dental pulp cells were cultured on the surface of the scaffolds for up to 21 days and examined using various assays. Cell proliferation and mineralization were examined using Alamar Blue and Xylenol Orange (XO) staining assays, respectively. The differentiation of pulp cells into odontoblasts was examined by immunostaining for Nestin and by quantitative PCR analysis for dentin matrix protein 1 (Dmp1), dentin sialophosphoprotein (Dspp) and osteocalcin (Ocn). Our results showed that the highest tubular density scaffolds significantly (p<0.05) enhanced differentiation of pulp cells into odontoblasts as compared to control flat scaffolds, as evidenced by increased expression of Nestin (5.4x). However, mineralization was suppressed on all surfaces, possibly due to low cell density. These results suggest that the microtubular architecture may be a desirable feature of scaffolds developed for clinical applications.

LAY SUMMARY

Regenerative engineering of diseased or traumatized tooth structure could avoid the deficiencies of traditional dental restorative (filling) materials. Cells in the dental pulp have the potential to differentiate to dentin-producing odontoblast cells. Furthermore, cell-supporting scaffolds that mimic a natural extracellular matrix (ECM) are known to influence behavior of progenitor cells. Accordingly, we hypothesized that a dentin-like microtubular scaffold would enhance differentiation of dental pulp cells. The hypothesis was proven true and differentiation to odontoblasts increased with increasing density of the microtubules. However, mineralization was suppressed, possibly due to a low density of cells. The results demonstrate the potential benefits of a microtubular scaffold design to promote odontoblast cells for regeneration of dentin.

Human Dental Pulp Facilitates Bone Regeneration in a Rat Bone Defect Model

The objective of this work was to investigate the osteogenetic ability of the human dental pulp stem cells (hDPSCs) derived from human third molars. We induced alkaline phosphatase (ALP) activity and bone morphogenetic protein 2 (BMP-2) mRNA expression, the markers for bone formation, in hDPSCs by using osteoinductive factors. The implantation of hDPSCs with collagen sponge promoted osteogenesis and fracture healing in the femur of an immunocompromised rat, which was a bone defect model for pseudoarthrosis. Histological analyses revealed that after implantation of the hDPSCs, the size and number of osteoblasts and the rates of osteoid production and mineralization increased to an appreciable extent, whereas the rate of bone resorption decreased. We believe that hDPSC implantation is a simple and safe procedure that can be beneficial in bone regeneration therapy in clinical practice.

A feasibility study for the analysis of reparative dentinogenesis in pOBCol3.6GFPtpz transgenic mice

AIM

To examine the feasibility of using the pOBCol3.6GFPtpz [3.6-green fluorescent protein (GFP)] transgenic mice as an in vivo model for studying the biological sequence of events during pulp healing and reparative dentinogenesis.

METHODOLOGY

Pulp exposures were created in the first maxillary molar of 12-16-week-old 3.6-GFP transgenic mice with CD1 and C57/Bl6 genetic background. Direct pulp capping on exposed teeth was performed using mineral trioxide aggregate followed by restoration with a light-cured adhesive system (AS) and composite resin. In control teeth, the AS was placed in direct contact with the pulp. Animals were euthanized at various time points after pulp exposure and capping. The maxillary arch was isolated, fixed and processed for histological and epifluorescence analysis to examine reparative dentinogenesis.

RESULTS

Analysis of teeth immediately after pulp exposure revealed absence of odontoblasts expressing 3.6-GFP at the injury site. Evidence of reparative dentinogenesis was apparent at 4 weeks in 3.6-GFP mice in CD1 background and at 8 weeks in 3.6-GFP mice with C57/Bl6 background. The reparative dentine with both groups contained newly formed atubular-mineralized tissue resembling a dentine bridge and/or osteodentine that was lined by cells expressing 3.6-GFP as well as 3.6-GFP expressing cells embedded within the atubular matrix.

CONCLUSION

This study was conducted in a few animals and did not allow statistical analysis. The results revealed that the 3.6-GFP transgenic animals provide a unique model for direct analysis of cellular and molecular mechanisms of pulp repair and tertiary dentinogenesis in vivo. The study also shows the effects of the capping material and the genetic background of the mice in the sequence and timing of reparative dentinogenesis.

Behaviour of rat-cultured dental pulp cells in three-dimensional collagen type-1 gel in vitro and in vivo

The purpose of this study was to investigate the growth and differentiation potential of dental pulp cells (DPCs) in three-dimensional (3-D) collagen type-1 scaffold in vitro and in vivo. Third passage DPCs were cultured in a 3-D collagen and expression of both bone- or dentin-related mRNA (alkaline phosphatase (ALP), bone sialoprotein (BSP) and osteopontin (OPN)) and morphological changes evaluated in vitro. In the in vivo study, two types of grafts were transplanted into the rectus abdominus muscles of rats and harvested after 7 days: DPCs in α-minimal essential medium and DPCs mixed with a collagen gel. ALP, BSP and OPN were used as primary antibodies for immunohistochemical study. Histological and immunohistochemical results showed that DPCs in collagen gel were spindle shaped and showed significantly greater expression of ALP, BSP and OPN in vitro than the controls. Transplanted DPCs in collagen type-1 gel showed greater positive immunoreactivity for ALP, BSP and OPN than the controls. It was concluded that the collagen gel scaffold encouraged the differentiation of DPCs into osteoblastic cells.

Odontoblast-targeted Bcl-2 overexpression promotes dentine damage repair

OBJECTIVE

Bcl-2 is widely expressed in a developing tooth organ and regulates tooth morphogenesis. However, whether Bcl-2 is related to tooth damage repair is unknown yet. Using an odontoblast-targeted Bcl-2 overexpression transgenic mouse (Col2.3Bcl-2) and artificial cavity preparation as a model system, the relationship between Bcl-2 and reparative dentinogenesis is investigated in this study.

METHODS

The odontoblastic-like cell cultures derived from mouse molar pulps were established. The expression of transgenic human Bcl-2 (hBcl-2) and endogenous mouse Bcl-2 (mBcl-2) and mouse Bax (mBax, a Bcl-2 antagonist) was detected in vivo and in vitro by Western blot and immunocytochemistry, respectively. Basal level and artificial cavity-induced odontoblast apoptosis was detected by the Deoxynucleotidyl Transferase (TdT) dUTP Nick End labelling (TUNEL) technique. Reparative dentine formation induced by artificial cavity drilled to a half dentine thickness on mesial cervical region of mandibular first molars 2, 4, and 6 weeks post-op was evaluated histologically and via micro-CT.

RESULTS

The transgenic hBcl-2 was stably expressed in odontoblasts of the transgenic animals without interference with the expression of mBcl-2 and mBax. Basal level as well as artificial cavity- induced odontoblast apoptosis was prevented by the transgene. Compared to the wild type, the transgenic animals produced reparative dentine with significantly higher mineral density 6 weeks after the operation.

CONCLUSIONS

Bcl-2 overexpression prevents odontoblast apoptosis and promotes dentine damage repair, indicating that genetic manipulation of Bcl-2 may be a novel strategy to maintain the vitality and function of dentine-pulp complex under detrimental mechanical stimuli.

Identification of secretory odontoblasts using DMP1-GFP transgenic mice

Terminal differentiation of odontoblasts from dental papilla is a long process involving several intermediate steps and changes in the transcriptional profile and expression of proteins secreted by cells in the odontoblast lineage. Transgenic mouse lines in which GFP expression is under the control of tissue- and stage specific promoters have provided powerful experimental tools for identification and isolation of cells at specific stages of differentiation along a lineage. Our previous studies showed utilization of pOBCol3.6GFP and pOBCol2.3GFP animals for identification of odontoblasts at early and late stages of polarization respectively. In the present study we used the DMP1-GFP transgenic animal as an experimental model to examine its expression during the differentiation of odontoblasts from progenitor cells in vivo and in vitro. Our observations showed that DMP1-GFP transgene is first activated in secretory/functional odontoblasts engaged in secretion of predentin and then transiently expressed at high levels in newly differentiated odontoblasts. Expression of DMP1-GFP was down-regulated in highly differentiated odontoblasts. The temporal and spatial pattern of expression of DMP1-GFP transgene closely mimics the expression of endogenous DMP1. This transgenic animal will facilitate studies of gene expression and biological functions in secretory/functional odontoblasts.

Identification of cells at early and late stages of polarization during odontoblast differentiation using pOBCol3.6GFP and pOBCol2.3GFP transgenic mice

Transgenic mouse lines in which GFP expression is under the control of tissue- and stage specific promoters have provided powerful experimental tools for identification and isolation of cells at specific stage of differentiation along a lineage. In the present study, we used primary cell cultures derived from the dental pulp from pOBCol3.6GFP and pOBCol2.3GFP transgenic mice as a model to develop markers for early stages of odontoblast differentiation from progenitor cells. We analyzed the temporal and spatial expression of 2.3-GFP and 3.6-GFP during in vitro mineralization. Using FACS to separate cells based on GFP expression, we obtained relatively homogenous subpopulations of cells and analyzed their dentinogenic potentials and their progression into odontoblasts. Our observations showed that these transgenes were activated before the onset of matrix deposition and in cells at different stages of polarization. The 3.6-GFP transgene was activated in cells in early stages of polarization, whereas the 2.3-GFP transgene was activated at a later stage of polarization just before or at the time of formation of secretory odontoblast.

Characterization of stem and progenitor cells in the dental pulp of erupted and unerupted murine molars

In the past few years there have been significant advances in the identification of putative stem cells also referred to as "mesenchymal stem cells" (MSC) in dental tissues including the dental pulp. It is thought that MSC in dental pulp share certain similarities with MSC isolated from other tissues. However, cells in dental pulp are still poorly characterized. This study focused on the characterization of progenitor and stem cells in dental pulps of erupted and unerupted mice molars. Our study showed that dental pulps from unerupted molars contain a significant number of cells expressing CD90+/CD45-, CD117+/CD45-, Sca-1+/CD45- and little if any CD45+ cells. Our in vitro functional studies showed that dental pulp cells from unerupted molars displayed extensive osteo-dentinogenic potential but were unable to differentiate into chondrocytes and adipocytes. Dental pulps from erupted molars displayed a reduced number of cells, contained a higher percentage of CD45+ and a lower percentage of cells expressing CD90+/CD45-, CD117+/CD45- as compared to unerupted molars. In vitro functional assays demonstrated the ability of a small fraction of cells to differentiate into odontoblasts, osteoblasts, adipocytes and chondrocytes. There was a significant reduction in the osteo-dentinogenic potential of the pulp cells derived from erupted molars compared to unerupted molars. Furthermore, the adipogenic and chondrogenic differentiation of pulp cells from erupted molars was dependent on a long induction period and were infrequent. Based on these findings we propose that the dental pulp of the erupted molars contain a small population of multipotent cells, whereas the dental pulp of the unerupted molars does not contain multipotent cells but is enriched in osteo-dentinogenic progenitors engaged in the formation of coronal and radicular odontoblasts.

Root dentin body moisture changes caused by ascorbic acid

OBJECTIVES

To quantify in vitro the root dentin moisture (DM) when soaked in 10% ascorbic acid solution (Group A) and distilled water (Group B) for up to 14 days.

METHODS

Forty-four extracted human mandibular single-rooted teeth were sectioned perpendicular to the long axis at the CEJ to access the root dentin. The samples were divided into Groups A and B. Baseline (day 0) DM was measured using a digital grain moisture meter. One sample was placed in each tube, which was then filled with solution. All tubes were kept at 37 degrees C and 100% humidity. DM was measured after 1, 3, 7, and 14 days. The baseline DM value was used as a covariate in the generalized estimating equation (GEE) analysis to account for the difference in the baseline DM between the two groups.

RESULTS

The mean DM (%) values+/-standard deviation on days 0, 1, 3, 7, and 14 were 11.4+/-1.08, 17.1+/-0.87, 18.2+/-0.76, 18.4+/-0.77, and 17.9+/-0.90 in Group A, and 10.2+/-0.95, 12.8+/-0.90, 13.3+/-0.95, 13.0+/-0.91, and 13.2+/-0.89 in Group B, respectively. Group A had significantly higher baseline DM than Group B (p=0.006). After adjusting for differences in the baseline, the GEE analysis indicated that, on average, Group A had a significantly higher increase in DM than Group B, with means+/-standard deviation of 4.35+/-0.26.

CONCLUSIONS

The moisture increase in the ascorbic acid group was greater than that in the distilled water group. Soaking root dentin in the unreplenished ascorbic acid solution or distilled water beyond 3 days did not further increase DM.