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


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.


CONCLUSIONS
These results suggest that fibulin-5 up-regulated in response to tension strain may control the formation of microfibril bundles in periodontal ligament.
Nakashima
K
K
Section of Orthodontics, Department of Oral Growth & Development, Division of Clinical Dentistry, Fukuoka Dental College, Tamura, Sawara-ku, Fukuoka, Japan.
Tsuruga
E
E
Hisanaga
Y
Y
Ishikawa
H
H
Sawa
Y
Y
D015152:Blotting, Northern; D015153:Blotting, Western; D002478:Cells, Cultured; D004547:Elastic Tissue / Q000166:cytology / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000032:analysis / Q000378:metabolism*; D000071838:Fibrillin-1; D000071837:Fibrillins; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006801:Humans; D020894:Microfibrils / Q000502:physiology* / Q000648:ultrastructure; D008840:Microfilament Proteins / Q000032:analysis / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D010513:Periodontal Ligament / Q000166:cytology* / Q000378:metabolism; D034741:RNA, Small Interfering; D013314:Stress, Mechanical; D015854:Up-Regulation; D054392:Adipokines
D016326:Extracellular Matrix Proteins; D000071838:Fibrillin-1; D000071837:Fibrillins; D008840:Microfilament Proteins; D034741:RNA, Small Interfering; C492373:FBLN5 protein, human; C000605722:FBN1 protein, human; D054392:Adipokines; C437744:oxytalan