Flow cytometry analysis of guided tissue regeneration-associated human periodontal cells

Barrier membranes: More than the barrier effect?

AIM

To review the knowledge on the mechanisms controlling membrane-host interactions in guided bone regeneration (GBR) and investigate the possible role of GBR membranes as bioactive compartments in addition to their established role as barriers.

MATERIALS AND METHODS

A narrative review was utilized based on in vitro, in vivo and available clinical studies on the cellular and molecular mechanisms underlying GBR and the possible bioactive role of membranes.

RESULTS

Emerging data demonstrate that the membrane contributes bioactively to the regeneration of underlying defects. The cellular and molecular activities in the membrane are intimately linked to the promoted bone regeneration in the underlying defect. Along with the native bioactivity of GBR membranes, incorporating growth factors and cells in membranes or with graft materials may augment the regenerative processes in underlying defects.

CONCLUSION

In parallel with its barrier function, the membrane plays an active role in hosting and modulating the molecular activities of the membrane-associated cells during GBR. The biological events in the membrane are linked to the bone regenerative and remodelling processes in the underlying defect. Furthermore, the bone-promoting environments in the two compartments can likely be boosted by strategies targeting both material aspects of the membrane and host tissue responses.

Highly osteogenic PDL stem cell clones specifically express elevated levels of ICAM1, ITGB1 and TERT

Cells derived from the periodontal ligament (PDL) have previously been reported to have stem cell-like characteristics (PDL stem cells; PDLSCs) and play an important part in bone engineering, including that of alveolar bone. However, these populations have been heterogeneous, and thus far no specific marker has yet been established from adult human stem cells derived from PDL tissue. We have previously isolated highly purified single cell-derived PDLSC clones and delineated their phenotypic and functional characteristics. In this report, we further obtained three homogeneous and distinct PDLSC clones demonstrating low, moderate and high mineralized matrix forming ability-namely PC12, PC4 and PC3, respectively, and the expression of mesenchymal stem cell pathway-specific genes in these clones was investigated. PCR array revealed that the expression of intercellular adhesion molecule 1 (ICAM1), integrin beta 1 (ITGB1) and telomerase reverse transcriptase (TERT) was associated with highly osteogenic PDLSC clones, as determined by the expression of key osteoblastic markers and their ability to form alizarin red S positive mineralized matrix in vitro. The present results suggest that these three mesenchymal stem cell-associated markers could potentially be used to isolate PDLSCs with high osteogenic capability for engineering new bone.

Evaluation of steroid hormone receptor protein expression in intact cells using flow cytometry

Several methods are currently employed to evaluate expression of steroid hormone receptors in tissues and cells, including real-time reverse-transcriptase polymerase chain reaction (real-time RT-PCR) and western blot assays. These methods require homogenization of cells, thereby preventing evaluation of individual cells or specific cell types in a given tissue sample. In addition, methods such as real-time RT-PCR assess mRNA levels, which may be subject to posttranslational modifications that prevent subsequent production of functional proteins. Flow cytometry is a fluorescence-based technique commonly used to evaluate expression of cell surface and intracellular proteins. This method is especially useful as it allows for single-cell analysis and can be utilized to determine the amount of receptor expressed by individual cells. Flow cytometry is commonly used to analyze immune cell activity and determine functionality based on changes in expression of cell surface molecules, as well as intracellular proteins (such as cytokines). Here, we describe a method to identify protein expression of steroid hormone receptors by rat leukocytes from different organs (spleen, liver and thymus) using flow cytometry. We examined expression of glucocorticoid receptor (GR), androgen receptor (AR) and progesterone receptor (PR) by cells at these sites and were able to demonstrate expression of receptors, as well as the intensity of expression of each receptor. This method is useful for rapid, high throughput measurement of steroid hormone receptors at the protein level in single, intact cells and would be valuable to determine which cells are more likely to respond to steroid hormone treatment.

Up-regulation of bone morphogenetic protein receptor IB by growth factors enhances BMP-2-induced human bone cell functions

Bone morphogenetic proteins (BMP) stimulate osteoblast differentiation by signal transduction via three BMP receptors (BMPR-IA, -IB, and -II). Several growth factors, including transforming growth factor-beta1 (TGF-beta1), fibroblast growth factor-2 (FGF-2) and platelet-derived growth factor-AB (PDGF-AB), have also been shown to play an important part in osteogenesis. The mechanism underlying these activities is unclear, but these growth factors could modulate the BMP/BMPR pathway by up-regulating BMPR expression, thereby enhancing the osteogenic responses of bone cells to the BMP. In this study we have therefore examined the effects of TGF-beta1, FGF-2, and PDGF-AB on BMPR expression and BMP-2-mediated osteoblast functions in primary human bone cells. The results showed that although the ligand BMP-2 and growth factors had little effect on BMPR-IA and -II transcript expression, they significantly up-regulated BMPR-IB mRNA specifically. However, only the growth factors, but not the ligand BMP-2, increased the surface expression of the BMPR-IB antigen, which was found to be due to a differential effect of BMP-2 and the growth factors on the Smurf1/Smad6-induced breakdown process. Pre-incubation of the cells with the growth factors significantly augmented BMP-2-induced Smad1/5/8 phosphorylation, and Dlx5 expression ALP activity, compared with that of cells treated with BMP-2 alone. When cells were transfected with siRNA targeting BMPR-IB, the growth factors neither up-regulated BMPR-IB transcript expression nor enhanced BMP-2-induced Smad1/5/8 phosphorylation, Dlx5 expression and ALP activity. The results indicate that increased BMPR-IB by TGF-beta1, FGF-2, and PDGF-AB significantly enhances BMP-2-induced osteogenic functions in vitro, suggesting that they might positively modulate bone formation by up-regulating BMPR-IB in vivo.

Shedding of a soluble form of BMP receptor-IB controls bone cell responses to BMP

Bone morphogenetic proteins (BMP) are members of the transforming growth factor beta (TGF-beta) superfamily and are involved in a wide variety of biological processes, including osteoblast differentiation and bone healing. The activities of the BMP are mediated by signal transduction via three BMP receptors (BMPR-IA, -IB and -II), which are thus essential for the biological actions of the BMP. Although the precise mechanisms which control the BMPR are not yet known, it is possible that post-translational regulation of these cell surface antigens by shedding could modulate their expression and thereby at least partly determine the response of the cells to the BMP. To test this possibility, the present study has examined whether soluble forms of the BMPR are produced by shedding from primary human bone cells in vitro. The results showed that human bone cells expressed both mRNA transcripts and antigens corresponding to BMPR-IA, -IB and -II. Incubation of the cells with phorbol 12-myristate 13-acetate (PMA), a potent inducer of proteolytic shedding, resulted in a pronounced decrease in cell surface expression of all three BMPR and, concurrently, the presence of "soluble" forms of these antigens in culture supernatants. Moreover, PMA treatment significantly reduced the level of BMP-2-induced Smad1/5 phosphorylation, a major early activation step in signal transduction initiated by BMP/BMPR interaction. It is notable that, while treatment of bone cells with interleukin-1beta (IL-1beta) also reduced the level of surface BMPR-IB, this inflammatory cytokine had no effect on BMPR-IA or -II levels, hence only the soluble form of BMPR-IB was detected. Furthermore, in addition to down-regulating BMP-2-induced Smad1/5 phosphorylation, IL-1beta also caused a reduction in the level of BMP-2-induced alkaline phosphatase activity and osteocalcin expression, both closely associated with bone cell differentiation. In conclusion, our study has provided evidence, for the first time, that BMPR can be modulated at the cell surface by the shedding of a soluble form of the antigen, resulting in a markedly diminished response to BMP-2 in vitro.

Changes in Soluble Adhesion Molecules in Gingival Crevicular Fluid Following Periodontal Surgery

BACKGROUND

Inflammation of periodontal tissues during postoperative wound healing is mediated by cell surface adhesion molecules. Soluble forms of these antigens have also been identified and shown to be important in immunoregulatory processes, but have previously not been investigated during periodontal repair and regeneration. The present study has examined the presence and possible changes in soluble intercellular adhesion molecule-1 (sICAM-1; CD54) and lymphocyte function-associated antigen-3 (sLFA-3; CD58) in gingival crevical fluid (GCF) following periodontal surgery.

METHODS

GCF samples were collected from four groups: 1) a guided tissue regeneration (GTR) test; 2) a GTR control, at least one complete tooth unit away from the periodontal defect; 3) a conventional flap (CF) surgery; and 4) a crown lengthening (CL). Sandwich enzyme-linked immunosorbent assay (ELISA) was used to measure the levels of sICAM-1 and sLFA-3 in the GCF samples.

RESULTS

A marked increase in GCF volumes was found in all sites after surgery, although a persistent increase was associated only with the period of membrane retention at the GTR test sites. In addition, sICAM-1 and sLFA-3 were found in the GCF of healthy as well as diseased sites prior to treatment and the total amounts of both increased transiently following surgical intervention, especially sLFA-3. However, the concentrations of these GCF components, particularly sICAM-1, tended to decrease.

CONCLUSIONS

The temporal decrease in the concentration of sICAM-1 and sLFA-3 in GCF may serve to enhance inflammatory reactions at surgically-treated periodontal sites, thereby limiting repair and regeneration in the periodontium. These soluble adhesion molecules may thereby be of potential therapeutic value and might also be useful markers for monitoring periodontal wound healing.

Expression of growth factors in the gingival crevice fluid of patients with phenytoin-induced gingival enlargement

The mechanism underlying phenytoin (PHT)-induced gingival enlargement (GE) is not yet known. The aim of the present study was to investigate transforming growth factor-beta1 (TGF-beta1), platelet-derived growth factor-BB (PDGF-BB) and basic fibroblast growth factor (bFGF) profiles in the gingival crevice fluid (GCF) of patients with PHT-induced GE and to compare the results with healthy controls. Five PHT-treated patients and five healthy subjects with normal periodontal tissue were included in this study. GCF samples were collected from (i) enlarged gingival sites in patients receiving PHT (GE+); (ii) non-enlarged gingival sites in the same patients (GE-); (iii) normal gingival sites of healthy subjects (control). The levels of TGF-beta1, PDGF-BB and bFGF in the GCF samples were analysed by ELISA. The results showed that the total amounts of TGF-beta1 and PDGF-BB in the GE+ group were higher than in the GE- group and significantly higher than in the control group (P < 0.05). However, no significant differences were found between the groups when the concentrations of these growth factors were compared. bFGF levels were not compared as this growth factor could be detected in only 33, 41 and 44% of the GE+, GE- and control GCF samples, respectively. These results show that TGF-beta1 and PDGF-BB are readily detectable in GCF obtained from enlarged and non-enlarged sites of PHT recipients and suggest that since the amounts were markedly higher at the GE+ than the GE- sites, the systemic administration of PHT has a pronounced localised effect on the levels of these growth factors. Moreover, our findings provide evidence that both TGF-beta1 and PDGF-BB are closely associated with the clinical manifestation of PHT-induced GE.

Changes in transforming growth factor-beta1 in gingival crevicular fluid following periodontal surgery

OBJECTIVES

Growth factors play a major part in wound healing, including in the periodontium. However, the presence of growth factors in gingival crevicular fluid (GCF) in humans during periodontal wound healing has not yet been determined. Our hypothesis is that such factors are present in GCF and that changes in their levels might be of value as a prognostic marker of wound-healing activity and therapeutic progress following periodontal surgery. The aim of this study was therefore to measure transforming growth factor-beta1 (TGF-beta1) in GCF collected from sites that have undergone guided tissue regeneration (GTR) and conventional flap (CF) surgery and to compare these with GCF collected from unaffected healthy sites.

MATERIALS AND METHODS

GCF samples were collected, using filter paper strips, at baseline (pre-surgical) and then at intervals up to 26 weeks from 16 patients undergoing GTR and from 11 patients undergoing CF surgery. After elution and acid treatment, TGF-beta1 levels were measured by ELISA.

RESULTS

Treatment of periodontal defect sites significantly reduced the mean probing pocket depth (PPD) and improved the mean lifetime cumulative attachment loss (LCAL). Average GCF volumes also significantly increased at all sites at 2 weeks post-surgery and thereafter declined to baseline levels, except at the GTR test sites that were still elevated at 7 weeks. TGF-beta1 could be detected in almost all GCF samples, and 2 weeks after surgery, the average levels increased two-fold at the surgically treated but not at the control sites, which remained unchanged.

CONCLUSION

TGF-beta1 is readily detectable in GCF and increases transiently following periodontal surgery. This suggests that changes in the levels of this growth factor in GCF might be useful for monitoring the progress of periodontal repair and regeneration.