Immunohistochemical expression of fibrillin-1 and fibrillin-2 during tooth development

BACKGROUND AND OBJECTIVE

Oxytalan fibers are categorized as a microfibril assembly without elastin deposition, and are unique components in the periodontal ligament (PDL). However, little is known about their formation during PDL development. To clarify the mechanisms of oxytalan fiber formation in developing PDL, we performed immunohistochemical analysis to detect the direct expression of fibrillin-1 and fibrillin-2, which are major components of microfibrils.

MATERIAL AND METHODS

Frozen sections of lower molars from mice at several stages of growth were prepared without chemical fixation and decalcification using the film transfer method. Immunostaining was performed with anti-fibrillin-1 and -2, and anticytokeratin antibodies.

RESULTS

Fibrillin-1 was not expressed in the dental follicle during the crown forming stage. At postneonatal day 9, fibrillin-1 expression started with meshwork appearance between the epithelial cells from Hertwig's epithelial root sheath at the root dentin surface. Fibirillin-2 was detected much earlier than fibrillin-1 expression. Fibrillin-2 was expressed with a liner appearance, running parallel to the root axis in PDL, and was partially co-expressed with cytokeratin 14 expression in Hertwig's epithelial root sheath. Furthermore, we detected both fibrillin-1 and fibrillin-2 expression in human PDL. Fibrillin-1 was detected in fibers with a vertically oriented root axis in PDL. Fibrillin-2 was widely expressed in PDL, including around the epithelial cell rests of Malassez. Fibrillin-1 and fibrillin-2 were clearly co-expressed in thick fiber structures in human PDL.

CONCLUSION

Our results suggest that both fibrillin-1 and fibrillin-2 expression is required to form thick oxytalan fibers in PDL. Based on the expression patterns for fibrillin-1 and fibrillin-2, they have different functions during tooth root and PDL development. Early expression of fibrillin-2 may regulate dental epithelial cell behavior during root and PDL development.

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.