Ultrastructural localization of fibrillin-1 and fibrillin-2 in oxytalan fibers in periodontal ligament of Japanese Macaca fuscata monkey

Actin alpha 2, smooth muscle, a transforming growth factor-β1-induced factor, regulates collagen production in human periodontal ligament cells via Smad2/3 pathway

Background/purpose

Actin alpha 2, smooth muscle (ACTA2) is an actin isoform that forms the cytoskeleton. Actin plays a crucial role in numerous cellular functions. ACTA2 is a marker of functional periodontal ligament (PDL) fibroblasts and is upregulated by transforming growth factor-β1 (TGF-β1); however, the underlying function of ACTA2 in PDL tissue is unknown. We aimed to examine the localization and potential function of ACTA2 in PDL tissues and cells.

Materials and methods

RNA expression was determined using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and quantitative RT-PCR. Protein expression was determined using immunofluorescence staining and Western blot analysis. Soluble and insoluble collagen production was examined using the Sircol collagen assay and picrosirius red staining, respectively. Small interfering RNA (siRNA) was used for knockdown assay to examine the effect of ACTA2 in human PDL cells.

Results

ACTA2 expression was observed in human primary PDL cells and PDL cell line (2-23 cells). TGF-β1 upregulated ACTA2, collagen type Ⅰ alpha1 chain (COL1A1), periostin (POSTN), and fibrillin-Ⅰ(FBN1) expression and soluble and insoluble collagen production in 2-23 cells. However, ACTA2 depletion by siRNA strongly suppressed PDL-related gene expression and collagen production compared with those of TGF-β1-stimulated control cells. Furthermore, ACTA2 knockdown significantly suppressed the phosphorylation of Smad2 and Smad3.

Conclusion

ACTA2 plays a crucial role in PDL-related marker expression and collagen production via Smad2/3 phosphorylation. Our findings might contribute to the development of novel and effective periodontal therapies.

Decreased Expression of Semaphorin3A/Neuropilin-1 Signaling Axis in Apical Periodontitis

Apical periodontitis (AP) is a chronic infection of endodontic origin accompanied with bone destruction around the apical region. Semaphorin3A (Sema3A) and neuropilin-1 (Nrp1) are regarded as a pair of immune regulators in bone metabolism. In this study, we firstly investigated the expression pattern of Sema3A/Nrp1 in apical periodontitis and its correlation with bone destruction. Using rat animal model, we analysed the level of mandibular bone destruction and the expression of Sema3A/Nrp1 on days 0, 7, 14, 21, 28, and 35 after pulp exposure. In addition, clinical samples from apical periodontitis patients were obtained to analyse the expression of Sema3A/Nrp1. These results indicated that the bone destruction level expanded from days 7 to 35. The number of positive cells and level of mRNA expression of Sema3A/Nrp1 were significantly decreased from days 7 to 35, with a negative correlation with bone destruction. Moreover, expression of Sema3A/Nrp1 in the AP group was reduced compared to the control group of clinical samples. In conclusion, decreased expression of Sema3A/Nrp1 was observed in periapical lesions and is potentially involved in the bone resorption of the periapical area, suggesting that Sema3A/Nrp1 may contribute to the pathological development of apical periodontitis.

Wnt5a suppresses osteoblastic differentiation of human periodontal ligament stem cell-like cells via Ror2/JNK signaling

Wnt5a, a non-canonical Wnt protein, is known to play important roles in several cell functions. However, little is known about the effects of Wnt5a on osteoblastic differentiation of periodontal ligament (PDL) cells. Here, we examined the effects of Wnt5a on osteoblastic differentiation and associated intracellular signaling in human PDL stem/progenitor cells (HPDLSCs). We found that Wnt5a suppressed expression of bone-related genes (ALP, BSP, and Osterix) and alizarin red-positive mineralized nodule formation in HPDLSCs under osteogenic conditions. Immunohistochemical analysis revealed that a Wnt5a-related receptor, receptor tyrosine kinase-like orphan receptor 2 (Ror2), was expressed in rat PDL tissue. Interestingly, knockdown of Ror2 by siRNA inhibited the Wnt5a-induced downregulation of bone-related gene expression in HPDLSCs. Moreover, Western blotting analysis showed that phosphorylation of the intracellular signaling molecule, c-Jun N-terminal kinase (JNK) was upregulated in HPDLSCs cultured in osteoblast induction medium with Wnt5a, but knockdown of Ror2 by siRNA downregulated the phosphorylation of JNK. We also examined the effects of JNK inhibition on Wnt5a-induced suppression of osteoblastic differentiation of HPDLSCs. The JNK inhibitor, SP600125 inhibited the Wnt5a-induced downregulation of bone-related gene expression in HPDLSCs. Additionally, SP600125 inhibited the Wnt5a-induced suppression of the alizarin red-positive reaction in HPDLSCs. These results suggest that Wnt5a suppressed osteoblastic differentiation of HPDLSCs through Ror2/JNK signaling. Non-canonical Wnt signaling, including Wnt5a/Ror2/JNK signaling, may function as a negative regulator of mineralization, preventing the development of non-physiological mineralization in PDL tissue.

Ultrastructural immunolocalization of laminin 332 (laminin 5) at dento-gingival interface in Macaca fuscata monkey

Although laminin 332 (laminin 5), an extracellular matrix molecule involved in cell adhesion and migration, has been localized at the interface between the tooth enamel and junctional epithelium, its ultrastructural localization remains to be fully clarified. The purpose of the present study was to investigate the ultrastructural distribution of laminin 332 at the dento-gingival interface in Japanese monkey (Macaca fuscata) using pre- and post-embedding immunoelectron microscopy. Pre-embedding immunoelectron microscopy revealed a broad band of internal basal lamina together with supplementary lamina densa, and both showed immunolabeling for laminin 332. Immunoreaction products for laminin 332 were observed in the rough-surfaced endoplasmic reticulum of the junctional epithelial cells close to the tooth enamel. Post-embedding immunoelectron microscopy revealed an increase in the number of immunogold particles toward the coronal portion, resulting in a large accumulation of particles on the basal lamina, preferentially on the lamina densa. Concomitantly the dental cuticle at the dento-gingival interface was sporadically, but specifically, immunogold-labeled with anti-laminin 332 antibody. These data suggest that junctional epithelium actively produces laminin 332, and that the products accumulate at the dento-gingival interface during cell migration coronally towards the gingival sulcus.

Matrix metalloproteinase-2 degrades fibrillin-1 and fibrillin-2 of oxytalan fibers in the human eye and periodontal ligaments in vitro

Oxytalan fibers are distributed in the eye and periodontal ligaments (PDL). The ciliary zonule, known as Zinn’s zonule, in the eye is composed of oxytalan fibers, which are bundles of microfibrils consisting mainly of fibrillin-1 and fibrillin-2. As turnover of oxytalan fibers is slow during life, their degradation mechanism remains unclarified. This study was performed to examine degradation pattern of fibrillin-1 and fibrillin-2 by experimental MMP activation. We cultured human non-pigmented ciliary epithelial cells (HNPCEC) and PDL fibroblasts for 7 days, then treated them with concanavalin A to activate matrix metalloproteinase (MMP)-2, and examined the degradation of fibrillin-1 and fibrillin-2 for 72 hr using immunofluorescence. At 7 days of HNPCEC culture, fibrillin-1-positive fibers were observed, some of which merged with fibrillin-2. After MMP-2 activation, fibrillin-1-positive fibers became thin and disappeared by 72 hr, while fibrillin-2-positive fibers disappeared almost completely within 24 hr. At 7 days of PDL fibroblast culture, fibrillin-1-positive fibers were mostly merged with fibrillin-2. After MMP-2 activation, fibrillin-1-positive fibers became thin by 24 hr and had almost disappeared by 48 hr, while fibrillin-2-positive fibers decreased constantly after 24 hr. A MMP-2 inhibitor completely suppressed these degradations. These results suggest that the patterns of fibrillin-1 and fibrillin-2 degradation differ between the eye and the PDL, possibly reflecting the sensitivity of fibrillin-1 and fibrillin-2 of each type of oxytalan fiber against MMP-2.

Exposure to transforming growth factor-β1 after basic fibroblast growth factor promotes the fibroblastic differentiation of human periodontal ligament stem/progenitor cell lines

Basic fibroblast growth factor (bFGF) is a cytokine that promotes the regeneration of the periodontium, the specialized tissues supporting the teeth. bFGF, does not, however, induce the synthesis of smooth muscle actin alpha 2 (ACTA2), type I collagen (COL1), or COL3, which are principal molecules in periodontal ligament (PDL) tissue, a component of the periodontium. We have suggested the feasibility of using transforming growth factor-β1 (TGFβ1) to induce fibroblastic differentiation of PDL stem/progenitor cells (PDLSCs). Here, we investigated the effect of the subsequent application of TGFβ1 after bFGF (bFGF/TGFβ1) on the differentiation of PDLSCs into fibroblastic cells. We first confirmed the expression of bFGF and TGFβ1 in rat PDL tissue and primary human PDL cells. Receptors for both bFGF and TGFβ1 were expressed in the human PDLSC lines 1-11 and 1-17. Exposure to bFGF for 2 days promoted vascular endothelial growth factor gene and protein expression in both cell lines and down-regulated the expression of ACTA2, COL1, and COL3 mRNA in both cell lines and the gene fibrillin 1 (FBN1) in cell line 1-11 alone. Furthermore, bFGF stimulated cell proliferation of these cell lines and significantly increased the number of cells in phase G2/M in the cell lines. Exposure to TGFβ1 for 2 days induced gene expression of ACTA2 and COL1 in both cell lines and FBN1 in cell line 1-11 alone. BFGF/TGFβ1 treatment significantly up-regulated ACTA2, COL1, and FBN1 expression as compared with the group treated with bFGF alone or the untreated control. This method might thus be useful for accelerating the generation and regeneration of functional periodontium.

Prospective potency of TGF-β1 on maintenance and regeneration of periodontal tissue

Periodontal ligament (PDL) tissue, central in the periodontium, plays crucial roles in sustaining tooth in the bone socket. Irreparable damages of this tissue provoke tooth loss, causing a decreased quality of life. The question arises as to how PDL tissue is maintained or how the lost PDL tissue can be regenerated. Stem cells included in PDL tissue (PDLSCs) are widely accepted to have the potential to maintain or regenerate the periodontium, but PDLSCs are very few in number. In recent studies, undifferentiated clonal human PDL cell lines were developed to elucidate the applicable potentials of PDLSCs for the periodontal regenerative medicine based on cell-based tissue engineering. In addition, it has been suggested that transforming growth factor-beta 1 is an eligible factor for the maintenance and regeneration of PDL tissue.

Development of the oxytalan fiber system in the rat molar periodontal ligament evaluated by light- and electron-microscopic analyses

In the elastic fiber system of the periodontal ligaments only oxytalan fibers can be identified, whereas all three types of fibers, oxytalan, elaunin and elastic fibers, are present in the gingiva. However, little information is available concerning their organization in the developing periodontal ligament. In the present study, growth and distribution of the oxytalan fiber system were examined in the developing periodontal ligament of rat molars using the specific staining for oxytalan, elastic and collagen fibers, and electron-microscopic analyses. Oxytalan staining clearly confirmed the earliest oxytalan fibers in a bell-staged tooth germ at embryonic day 18, which were tiny violet-colored fibers in the dental follicle. Their cross images were made up of dot-like microfibrils of 10-15nm in diameter close to fibroblasts in the dental follicle of the rat molars aged 1 day. These microfibrils appeared to be linked to one another through delicate filaments in 3-nm-diameter. At the beginning of root formation, the cross figures of oxytalan fibers were found as dot-like structures around the root sheath as well as in areas very close to blood vessels. As development proceeded, longer oxytalan fibers were produced in the apico-occlusal direction along with blood vessels. In addition, the immunoreactive products to anti-amyloid β protein on the surface of blood vessels suggest that this molecule might be involved in the adhesion of oxytalan fibers to vascular basement membranes. Thus, the oxytalan fiber system might regulate periodontal ligament function through tensional variations registered on the walls of the vascular structures.

Resorption of elastic fibers in monkey gingival connective tissue: ultrastructural and immunocytochemical evidence

Little is known about the remodeling of elastic fibers in gingival connective tissue. In this study, elastic fibers in the lamina propria of monkey gingiva were examined by transmission electron microscopy and immunocytochemistry. Some elastic fibers were localized at invagination on the surface of the narrow processes of fibroblasts distributed among dense assemblies of collagen fibrils, and also within coated pits, which were pinching off as coated vesicles. At a higher magnification, the coated vesicles contained filamentous structures, as well as pentagonal structures similar those previously reported in elastic fibers. Immunoelectron microscopy demonstrated positive staining for fibrillin, one of the main components of microfibril, localized either in the coated pits or vesicles. These observations indicate that at least some elastic fibers were resorbed by fibroblasts, and that, in spite of the general belief that little remodeling of elastic fibers occurs under normal conditions, resorption of elastic fibers does occur in monkey gingival connective tissue. The functional significance of this is not yet clear, but it may be involved in facilitating the delicate and efficient adaptation of tissue to physical requirements during mastication.