Kazuki Nakashima

Stretching modulates oxytalan fibers in human periodontal ligament cells

MATERIAL AND METHODS We subjected periodontal ligament fibroblasts to stretching strain to examine the effects on their formation of oxytalan fibers in cell/matrix layers. RESULTS Stretching increased the levels of fibrillin-1 and fibrillin-2 by 25% relative to the control, but did not affect the gene expression level of either type of fibrillin. Immunofluorescence and immunogold electron microscopy analysis revealed that bundles of oxytalan fibers became thicker under stretching conditions. CONCLUSION These results suggest that tension strain functionally regulates microfibril assembly in periodontal ligament fibroblasts and thus may contribute to the homeostasis of oxytalan fibers in periodontal ligaments.

Stretching stimulates fibulin-5 expression and controls microfibril bundles in human periodontal ligament cells.

BACKGROUND AND OBJECTIVE The elastic fiber system comprises oxytalan, elaunin and elastic fibers, differing in their relative microfibril and elastin contents. Human periodontal ligaments contain oxytalan fibers (pure microfibrils). Periodontal ligaments are continuously exposed to various functional forces, such as tooth movement and occlusal loading. We have reported that bundles of microfibrils coalesce in response to mechanical strain in cultured periodontal ligament fibroblasts, as assessed in terms of their positivity for fibrillin-1 (the major component of microfibrils). However, the mechanism of microfibril coalescence is unclear. We hypothesized that the fibrillin-1-binding molecule, fibulin-5, contributes to oxytalan fiber formation under mechanical strain. MATERIAL AND METHODS We subjected periodontal ligament fibroblasts to stretching in order to examine the effects of fibulin-5 on the formation of oxytalan fibers in cell/matrix layers. We transfected periodontal ligament cells with small interference RNA for fibulin-5, then examined oxytalan fibers using immunofluorescence and electron microscopy. RESULTS Immunofluorescence showed that fibrillin-1-positive microfibrils coalesced as a result of stretching, compared with cells that were not subjected to stretching. Fibulin-5 colocalized on fibrillin-1-positive microfibrils. Stretching increased fibulin-5 gene expression and protein deposition. Immunofluorescence and immunogold electron microscopy analysis revealed that fibulin-5 suppression inhibited the coalescence of microfibrils under stretching conditions. CONCLUSION These results suggest that fibulin-5 up-regulated in response to tension strain may control the formation of microfibril bundles in periodontal ligament.

Integrin αvβ3 regulates microfibril assembly in human periodontal ligament cells

Fibrillin-1 is the major structural component of extracellular microfibrils. However, the mechanism by which extracellular fibrillin-1 assembles into microfibrils is not fully understood. Fibrillin-1 contains the Arg-Gly-Asp (RGD) motif, which may allow binding to RGD-recognizing integrins. We hypothesized that integrin alphavbeta3 on the cell surface of human periodontal ligament (PDL) fibroblasts may influence fibrillin-1 assembly into cell/matrix layers. We treated PDL fibroblasts with an integrin alphavbeta3-specific antagonist to examine fibrillin-1 assembly. Western blotting and immunofluorescence analysis showed that treatment with the integrin alphavbeta3 antagonist at 5 muM clearly abolished fibrillin-1 deposition. These results provide for the first time evidence that integrin alphavbeta3 regulates extracellular assembly of fibrillin-1, thereby modulating cell-mediated homeostasis of microfibrils.

Fibulin-5 Contributes to Microfibril Assembly in Human Periodontal Ligament Cells

The elastic system fibers comprise oxytalan, elaunin and elastic fibers, which differ in their relative microfibril and elastin content. Human periodontal ligaments (PDL) contain only oxytalan fibers (pure microfibrils) among them. Since fibulin-5 regulates the organization of elastic fibers to link the fibers to cells, we hypothesized that fibulin-5 may contribute to the formation of oxytalan fibers. We used siRNA for fibulin-5 in PDL cell culture to examine the extracellular deposition of fibrillin-1 and -2, which are the major components of microfibrils. Fibulin-5 was labeled on microfibrils positive for fibrillin-1 and -2. Fibulin-5 suppression reduced the level of fibrillin-1 and -2 deposition to 60% of the control level. These results suggest that fibulin-5 may control the formation of oxytalan fibers, and play a role in the homeostasis of oxytalan fibers.

Fibulin-4 and -5, but not Fibulin-2, are Associated with Tropoelastin Deposition in Elastin-Producing Cell Culture

Elastic system fibers consist of microfibrils and tropoelastin. During development, microfibrils act as a template on which tropoelastin is deposited. Fibrillin-1 is the major component of microfibrils. It is not clear whether elastic fiber-associated molecules, such as fibulins, contribute to tropoelastin deposition. Among the fibulin family, fibulin-2, -4 and -5 are capable of binding to tropoelastin and fibrillin-1. In the present study, we used the RNA interference (RNAi) technique to establish individual gene-specific knockdown of fibulin-2, -4 and -5 in elastin-producing cells (human gingival fibroblasts; HGF). We then examined the extracellular deposition of tropoelastin using immunofluorescence. RNAi-mediated down-regulation of fibulin-4 and -5 was responsible for the diminution of tropoelastin deposition. Suppression of fibulin-5 appeared to inhibit the formation of fibrillin-1 microfibrils, while that of fibulin-4 did not. Similar results to those for HGF were obtained with human dermal fibroblasts. These results suggest that fibulin-4 and -5 may be associated in different ways with the extracellular deposition of tropoelastin during elastic fiber formation in elastin-producing cells in culture.

EMILIN-1 regulates the amount of oxytalan fiber formation in periodontal ligaments in vitro

The elastic system fibers comprise oxytalan, elaunin, and elastic fibers, differing in their relative microfibril and elastin contents. Among them, human periodontal ligament (PDL) contains only oxytalan fibers (pure microfibrils). Elastin microfibril interface-located protein-1 (EMILIN-1) is localized at the interface between microfibrils and elastin. We hypothesized that EMILIN-1 may contribute to the formation of oxytalan fibers. We used a small interfering RNA (siRNA) for EMILIN-1 in PDL cell culture to examine the extracellular deposition of fibrillin-1 (the major component of microfibrils). EMILIN-1 was labeled on microfibrils positive for fibrillin-1 and was colocalized with fibrillin-1 upon immunoprecipitation assay. EMILIN-1 suppression reduced the level of fibrillin-1 deposition to 23% of the control, and this was responsible for the diminution of fibrillin-1 deposition revealed by immunofluorescence. These results suggest that EMILIN-1 may regulate the formation of oxytalan fibers and play a role in their homeostasis.

Stretch stimuli increase fibulin-5/EMILIN-1 complex on oxytalan fibers in human periodontal ligament cells

Abstract Periodontal ligaments (PDLs) are continuously exposed to various functional forces, such as tooth movement and occlusal loading. Human PDLs comprise elastic system fibers as well as collagen fibers. The elastic system fibers in turn comprise oxytalan, elaunin and elastic fibers, which differ in their relative microfibril and elastin contents. Human PDLs contain oxytalan fibers (pure microfibrils), which are composed mainly of fibrillin-1 (the major component of microfibrils). We have previously reported that bundles of oxytalan fibers in cultured PDL cells coalesce in response to mechanical strain, and that this coalescence is controlled by fibulin-5. However, the relationship between fibulin-5 and other fibrillin-1-binding molecules is unclear. In the present study we investigated whether fibulin-5 and EMILIN-1 (both of which are fibrillin-1-binding molecules) contribute to the formation of oxytalan fibers upon exposure to mechanical strain. We subjected PDL cells to stretching in order to examine the role of fibulin-5 and EMILIN-1 in the formation of oxytalan fibers in cell/matrix layers. We examined the relationship between fibulin-5 and EMILIN-1 in PDL cell cultures using immunofluorescence and immunoprecipitation assay. Immunofluorescence showed that fibulin-5 and EMILIN-1 were colocalized on fibrillin-1-positive oxytalan fibers. Fibulin-5 formed a complex with EMILIN-1, and stretching increased the amount of this complex relative to cells that were not subjected to stretching. These results suggest that the expression of the fibulin-5/EMILIN-1 complex is upregulated in response to tension strain, and may control the formation of oxytalan fibers in PDLs.

Intracellular interaction of EMILIN-1 with fibrillin-1 in human periodontal ligament cells

Abstract The elastic system fibers comprise oxytalan, elaunin and elastic fibers, differing in their relative microfibril and elastin contents. Human periodontal ligaments (PDLs) contain oxytalan fibers (pure microfibrils), which are composed mainly of fibrillin-1, the major component of microfibrils. We recently demonstrated that EMILIN-1, located at the interface between elastin and microfibrils, controls the amount of fibrillin-1 assembly in PDL fibroblast cell/matrix layers [8], although the mechanism involved was unclear. We subjected cultured PDL fibroblasts to immunofluorescence and immunoprecipitation assays in order to examine the intracellular interaction of EMILIN-1 with fibrillin-1. Immunofluorescence showed that EMILIN-1 was colocalized with fibrillin-1, both inside and outside the cells. Additionally, EMILIN-1 formed a complex with fibrillin-1 in the intracellular fraction. These results suggest that EMILIN-1 may form complexes with fibrillin-1 in cellular vesicles, thus contributing effectively to the initial assembly of pericellular fibrillin-1 during the process of oxytalan fiber formation.